CCIE Routing & Switching Advanced Technologies Class

Transcript

1	Introduction	0h 43m
2	Using the Cisco Documentation	0h 52m
3	Ethernet Overview, Layer 2 Switchports, Trunking, ISL, 802.1q, DTP	0h 47m
4	VTP, VTP Authentication, VTP Pruning	1h 02m
5	VTP Prune Eligible List, VTP Transparent, VTP Troubleshooting, Trunk Allowed List, Extended VLANs	0h 48m
6	VLAN and VTP Review	0h 19m
7	SVIs, Native Routed Interfaces, Router-on-a-Stick	0h 46m
8	Layer 2 EtherChannel, EtherChannel Load Balancing, Layer 3 EtherChannel	0h 57m
9	802.1q Tunneling, Layer 2 Protocol Tunneling, EtherChannel over 802.1q Tunneling	1h 03m
10	STP Root Bridge Election, STP Root Port Election, STP Designated Port Election, STP Priority, STP Cost, STP Port-Priority	1h 46m
11	STP Review	0h 12m
12	STP Timers, STP PortFast	0h 34m
13	STP UplinkFast	0h 11m
14	STP BackboneFast	0h 12m
15	STP BPDU Filter	0h 13m
16	STP BPDU Guard	0h 11m
17	STP Root Guard	0h 11m
18	STP Loop Guard, Unidirectional Link Detection (UDLD)	0h 11m
19	Multiple Spanning-Tree Protocol (MST)	0h 40m
20	Rapid Spanning-Tree Protocol (RSTP), Rapid-PVST	0h 18m
21	MST with Multiple Regions	0h 33m
22	Flex Links	0h 16m
23	Frame Relay	0h 39m
24	Frame Relay Configuration Part 1	0h 34m
25	Frame Relay Configuration Part 2	0h 41m
26	Frame Relay Switching	0h 27m
27	Back-to-Back Frame Relay	0h 08m
28	Frame-Relay End-to-End Keepalives	0h 18m
29	PPP, PPP PAP Authentication, PPP CHAP Authentication	0h 59m
30	PPPoFR, PPPoE	0h 40m
31	Transparent Bridging, IRB	0h 32m
32	Fallback Bridging	0h 14m
33	IP Routing Overview, Switching Paths, Static Routing	0h 42m
34	Static Routing Examples	0h 25m
35	IP Default-Gateway, IP Default-Network	0h 14m
36	On-Demand Routing (ODR)	0h 07m
37	Floating Static Routes	0h 10m
38	Backup Interface	0h 29m
39	Enhanced Object Tracking, IP SLA, Reliable Static Routing	0h 21m
40	Policy Routing	0h 43m
41	GRE Tunneling, GRE Recursive Routing Errors	0h 27m
42	Reliable Backup Interface with GRE	0h 25m
43	RIP Overview, RIP Versions, RIP Auto-Summary	0h 48m
44	RIP Split-Horizon, RIP Timers	0h 22m
45	RIP Broadcast Updates, IP Directed Broadcast, IP Broadcast-Address, Smurf Attacks, Fraggle Attacks	0h 16m
46	RIP Unicast Updates	0h 03m
47	RIP Offset-List	0h 18m
48	RIP Authentication	0h 11m
49	RIP Summarization	0h 10m
50	Prefix-Lists, RIP Distribute-List Filtering, RIP Administrative Distance Filtering	0h 48m
51	RIP Default Routing, RIP Conditional Default Routing	0h 18m
52	RIP Triggered, RIP Validate Update Source,	0h 12m
53	EIGRP Overview	0h 29m
54	EIGRP Auto-Summary	0h 07m
55	EIGRP Split-Horizon	0h 11m
56	EIGRP Update Types, EIGRP Neighbor, EIGRP Passive-Interface	0h 24m
57	EIGRP Hello-Interval, EIGRP Hold-Time	0h 05m
58	EIGRP Authentication	0h 11m
59	EIGRP Time Based Authentication	0h 25m
60	EIGRP Path Selection, EIGRP Metric Weights, EIGRP Traffic Engineering	0h 47m
61	EIGRP Unequal Cost Load Balancing, EIGRP Variance	0h 19m
62	EIGRP QUERY, EIGRP Summarization, EIGRP Leak-Map	0h 28m
63	EIGRP Stub Router Advertisement	0h 22m
64	EIGRP Default Routing	0h 13m
65	EIGRP Route Filtering	0h 11m
66	EIGRP Router-ID	0h 07m
67	Miscellaneous EIGRP Features	0h 02m
68	OSPF Overview	0h 27m
69	Establishing OSPF Adjacencies, Understanding the OSPF Database	0h 43m
70	OSPF Network Type Broadcast, OSPF DR/BDR Election, OSPF over NBMA, OSPF Network Type Non-Broadcast and Point-to-Multipoint	0h 56m
71	OSPF Network Type Point-to-Point, OSPF Network Type Mismatch	0h 13m
72	OSPF Network Type Point-to-Multipoint Non-Broadcast, OSPF Per Neighbor Cost	0h 17m
73	OSPF Network Type Loopback	0h 02m
74	OSPF Path Selection	0h 27m
75	OSPF Convergence Timers	0h 09m
76	OSPF Authentication	0h 12m
77	OSPF Summarization	0h 32m
78	OSPF Stub Areas, OSPF Totally Stubby Areas, OSPF NSSAs, OSPF Totally NSSAs	0h 40m
79	Controlling OSPF NSSA Redistribution	0h 02m
80	OSPF Type 7 to 5 Translator Election, OSPF LSA Type 3 Filter, OSPF Forwarding Address Suppression	0h 24m
81	Route Redistribution Overview	0h 36m
82	Route Redistribution Configuration & Verification, Connected Redistribution	0h 22m
83	OSPF External Path Selection, TCL PING Scripting	0h 33m
84	Routing Loops Overview, EIGRP Route Loop Prevention	0h 55m
85	Metric Based Routing Loops, Route Tagging	0h 46m
86	Administrative Distance Based Routing Loops, Debug IP Routing, IP Route Profile	0h 58m
87	BGP Overview, BGP Peering Types	0h 51m
88	Establishing BGP Peerings, EBGP Multihop, BGP Neighbor Disable Connected Check, BGP TTL Security	0h 49m
89	BGP 4-Byte ASNs	0h 20m
90	BGP Local AS, BGP Peer Groups	0h 30m
91	BGP Next-Hop Self, BGP Next-Hop Processing	0h 30m
92	BGP Route Reflectors	0h 37m
93	Large Scale BGP Route Reflectors with Clusters	0h 34m
94	BGP Confederation	0h 37m
95	BGP NLRI Advertisements, BGP Network Statement, BGP Redistribution	0h 43m
96	BGP Aggregation, BGP Aggregation & Summary-Only, BGP Aggregation & Unsuppress-Map	0h 46m
97	BGP Origin, BGP Aggregation & AS-Set, BGP Aggregation & Advertise-Map	0h 22m
98	BGP Conditional Route Injection	0h 21m
99	BGP Bestpath Selection, BGP Multipath, BGP Weight	0h 53m
100	BGP Local Preference, BGP Local Preference and Communities, BGP AS-Path Prepending,	0h 30m
101	BGP MED, BGP MED Missing As Worst, BGP Deterministic MED	0h 34m
102	BGP Communites, BGP Regular Expressions	0h 43m
103	BGP Filtering, BGP Convergence Timers, BGP Default Routing, Miscellaneous BGP Features	0h 24m
104	MPLS Overview, MPLS Label Distribution Protocol (LDP)	1h 05m
105	MPLS Tunnels, MPLS Penultimate Hop Popping (PHP)	0h 40m
106	MPLS Layer 3 VPNs Overview, VRF Lite	0h 36m
107	MPLS Layer 3 VPNs and VPNv4 BGP	1h 08m
108	MPLS Layer 3 VPN Verification & Troubleshooting	0h 49m
109	MPLS Layer 3 VPN OSPF PE-CE Routing Overview	0h 06m
110	MPLS Layer 3 VPN OSPF PE-CE Routing Path Selection & Sham-Links	2h 01m
111	MPLS Layer 3 VPN OSPF PE-CE Routing Loop Prevention & Down-Bit, OSPF Capability VRF-Lite	0h 40m
112	IPv6 Overview, IPv6 ICMPv6 ND, IPv6 over NBMA	0h 44m
113	IPv6 Routing Overview, IPv6 Static Routing	0h 28m
114	IPv6 RIPng	0h 20m
115	IPv6 EIGRPv6	0h 09m
116	IPv6 OSPFv3	0h 31m
117	MP-BGP for IPv6	0h 26m
118	IPv6 Tunneling	1h 13m
119	Multicast Overview, IGMP	0h 34m
120	PIM Overview	0h 18m
121	PIM Dense Mode	1h 03m
122	PIM Sparse Mode	0h 30m
123	PIM Sparse Mode Configuration	0h 36m
124	PIM Sparse Mode RPF & RP Troubleshooting	0h 27m
125	Auto-RP, Multicast over GRE Tunnels	0h 53m
126	Bootstrap Router (BSR), Bidirectional PIM, Source Specific Multicast (SSM)	0h 40m
127	MSDP, Anycast RP	0h 27m
128	IPv6 Multicast Routing	0h 24m
129	QoS Overview, IntServ QoS, DiffServ QoS, IP Precedence, DSCP, MQC, HQF	0h 41m
130	MQC Classification	0h 44m
131	FIFO, FQ, WFQ, CBWFQ, HQF	0h 50m
132	LLQ	0h 23m
133	WRED	0h 31m
134	Traffic Shaping, Traffic Policing	0h 40m
135	Frame Relay Traffic Shaping (FRTS)	0h 33m
136	RSVP	0h 07m
137	Catalyst 3560 QoS	1h 00m
138	IOS Security Overview, Access Lists (ACLs)	0h 58m
139	Time Based ACLs, Dynamic ACLs	0h 33m
140	Reflexive ACLs	0h 21m
141	TCP Intercept, Content Based Access Control (CBAC)	0h 34m
142	Zone Based Policy Firewall (ZBPF)	1h 09m
143	AAA, Local Authentication, Local Authorization, Role Based CLI Access	0h 43m
144	Port Security, Static CAM Entries, Storm Control, 802.1X Authentication, PACLs, RACLs, VLAN Access Maps (VACLs)	0h 48m
145	DHCP Snooping, Dynamic ARP Inspection (DAI), IP Source Guard	0h 12m
146	Protected Ports, Private VLANs	0h 25m
147	IP Services Overview, HSRP	1h 10m
148	VRRP, GLBP	0h 28m
149	NAT	0h 42m
150	DHCP, DNS	0h 30m
151	NetFlow	0h 09m
152	WCCP, Miscellaneous IP Services	0h 06m
153	System Management Overview, NTP, NTP Authentication	0h 24m
154	SNMP, RMON	0h 38m
155	Syslog, Telnet, SSH, Banners	0h 21m
156	EEM Scripting, Miscellaneous System Management	0h 26m
Total Duration		81h 59m

Slides - Diagrams

Slides - Introduction

Slides - Ethernet Switching

Slides - Advanced Ethernet Switching

Slides - Frame Relay

Slides - PPP

Slides - Transport Bridging

Slides - Redistribution

Slides - IOS Security

Slides - Layer 2 Security

Slides - IP Services

Slides - System Management

0:00:14	Welcome back everybody to Internetwork Expert CCIE Routing and Switching Advanced Technologies class.
0:00:20	In today's sections, we're gonna be talking about IP Version 4 route redistribution.
0:00:25	What are the potential problems that we could run into with redistribution,
0:00:29	and how we can fix these problems with the design
0:00:32	before we actually see the end results in the network.
0:00:36	Now, overall, the lesson objectives that we're gonna have for....
0:00:41	today's session, first and foremost is gonna be to understand how the redistribution process works,
0:00:46	and what routes are candidate for redistribution
0:00:50	when we go between two different protocols.
0:00:52	So, for example, when we're redistributing between EIGRP and OSPF.
0:00:57	We'll also look at some common problems with doing redistribution of connected routes
0:01:03	whether we are explicitly doing a Redistribute Connected,
0:01:06	or whether we are implicitly doing this
0:01:08	when we are redistributing between the different dynamic protocols.
0:01:12	How IOS is gonna choose which routes it's gonna use
0:01:16	once redistribution occurs, and any type of problems that we can have with looping of the route redistribution.
0:01:24	Now, ideally, once we're done with this particular session in class,
0:01:28	everyone should have a good understanding of how to predict the type of looping in the network.
0:01:34	Be able to tell the difference between
0:01:36	topologies that will not cause redistribution problems,
0:01:39	and topologies that could potentially cause redistribution problems.
0:01:43	Then, how to predict these,
0:01:45	identify them, and the prevent the looping from occurring
0:01:49	in order for us to get full IP reachability between all devices in the topology.
0:01:55	Now, the first key point to understand about redistribution
0:01:59	is that the process of redistribution occurs from the routing table,
0:02:04	and not the routing database.
0:02:06	We'll see that this is gonna be significant
0:02:08	when we look at EIGRP, or RIP, or OSPF,
0:02:12	and we see a difference between what's installed in the EIGRP topology,
0:02:16	or the OSPF database versus what goes into the actual routing table.
0:02:22	So, when we're redistributing between two protocols,
0:02:25	if we're taking the source protocol X and redistributing it into the destination protocol Y,
0:02:30	the router is gonna first look at two things.
0:02:33	First, what are the routes that are actually installed in the routing information base,
0:02:37	or the routing table via that protocol,
0:02:40	and what are the connected interface in the routing table that are running that protocol.
0:02:48	Now, the first one is just gonna be controlled based on what particular prefixes we are learning.
0:02:53	In the case of EIGRP, this is gonna be any dynamic routes
0:02:56	that are coming from our connected peers whether these are internal routes or external routes.
0:03:03	The connected links that are running the protocol,
0:03:05	that's gonna be based on the network statement configured under the routing process
0:03:10	for either RIP, or EIGRP, or OSPF,
0:03:13	or for OSPF the IP OSPF command at the interface level.
0:03:19	So, when we look at the output of the Show IP Protocols on the IOS,
0:03:24	this should tell us what are the connected links
0:03:26	that are candidate to be redistributed between the different processes.
0:03:32	Now, we'll also see today that depending on what particular protocol we're looking at,
0:03:36	whether it's RIP, or BGP, or OSPF,
0:03:39	there are different rules that control
0:03:42	what particular routes we can install in the table
0:03:44	and then what particular routes that we can actually be advertised.
0:03:48	So, we need to know what are these normal design issues
0:03:52	with the different IGPs and BGP
0:03:56	before we can actually predict what's gonna happen inside the redistribution process.
0:04:03	Now, as I mentioned when the redistribution process happens here,
0:04:06	the router is gonna be looking for two things:
0:04:09	any dynamic routes installed in the routing table via that protocol,
0:04:13	so, for example if we are redistributing OSPF into EIGRP,
0:04:17	we're first gonna take any routes that show up any output of the Show IP Route OSPF.
0:04:23	Then, secondly, there is an implicit redistribution
0:04:26	that happens for any connected interfaces that are running the OSPF process.
0:04:32	Now, if we do not use the Redistribute Connected command,
0:04:35	then, any interfaces in this source protocol
0:04:39	that are directly connected into the destination protocol.
0:04:44	We'll see that the potential issue we'll run into
0:04:46	is that if we do explicitly list
0:04:49	what particular links will be redistributed from the connected process,
0:04:54	this is going to override what the implicit redistribution is.
0:05:00	So, if we were to take a look at the topology,
0:05:03	and let's say for example that on router 6,
0:05:08	we are running the RIP process to one of the backbone routers,
0:05:14	and we are running the OSPF process internal to our network.
0:05:20	And we wanna perform redistribution between RIP and OSPF on router 6.
0:05:25	So, when OSPF is going into RIP, the first thing router 6 is gonna do
0:05:29	is internally look at the output of the Show IP Route OSPF.
0:05:34	So, any dynamic routes that are learned in the Fast Ethernet 0/0.146,
0:05:39	or the Fast Ethernet 0/0.67,
0:05:42	those are gonna be candidate for redistribution.
0:05:46	Additionally, the connected links of the Fast Ethernet 0/0.146 and the .67 link,
0:05:53	whatever the IP prefix actually assigned to those interfaces are,
0:05:57	those should be candidate to be installed in the RIP database.
0:06:03	Now, the potential issue that we'll run into
0:06:05	is that if on router 6, under the RIP process,
0:06:09	if we were to issue a manual redistribute connected command,
0:06:13	then, this is going to automatically override
0:06:16	those interfaces that are coming from the OSPF process.
0:06:21	So, essentially, we need to treat the dynamic routing process as the connected routing process,
0:06:26	as two different entities from the prospective of redistribution.
0:06:32	As long as we do not manually issue the Redistribute Connected command,
0:06:35	then, we should assume that any interfaces directly connected that are running the protocol
0:06:40	will be sent to the destination protocol.
0:06:45	So, we'll take a look at some examples of the command line here
0:06:48	when the Connected Redistribution does work properly,
0:06:51	and then when we are filtering it with the Redistribute Connected command,
0:06:55	what are the potential problems that we could run into.
0:07:00	Now, once the router actually performs the redistribution,
0:07:03	then, it's gonna figure out which routes are actually gonna go into the routing table
0:07:09	depending on what the individual protocol we are running is.
0:07:14	So, first step is gonna look through the routing database
0:07:17	and figure out what are the candidate paths that can actually go in the routing table.
0:07:22	So, this is gonna depend on what that particular protocols, selection process is,
0:07:26	whether we're talking about the diffusing update algorithm for EIGRP,
0:07:31	or the shortest path first algorithm for OSPF,
0:07:34	we talked about those previously is gonna be specific to that individual protocol.
0:07:39	Now, once OSPF comes up with its candidate routes that can go in the routing table,
0:07:45	there could potentially be multiple paths
0:07:48	if they have equal metric values,
0:07:51	or in the case of EIGRP if we are configured for doing unequal cost load balancing.
0:07:57	But in the end, the routing database is gonna come up with a list
0:08:00	of what are the candidate routes that I can install in the routing table.
0:08:04	Then, the router is gonna look at,
0:08:07	are there multiple matches for these exact prefixes from different protocols.
0:08:13	So, for example, if I were to have the prefix 1.2.3.0/24,
0:08:18	and I'm learning it via both EIGRP and OSPF,
0:08:22	then, I'm gonna have to choose which one actually goes into the routing table.
0:08:26	And this is gonna be based on the administrative distance value.
0:08:30	So, whichever source protocol has the lower AD,
0:08:34	or the lower administrative distance, that's gonna be the one that is candidate to go into the routing information base,
0:08:40	which is the routing table.
0:08:41	And the forwarding information base, which is the CEF table.
0:08:46	Now, we talked about this previously what are the different administrative distance values for the protocols.
0:08:51	But we do need to take this into account anytime we are doing redistribution.
0:08:56	The reason why is we can see here
0:08:59	some of the IGPs and BGP treats the internal prefixes differently
0:09:05	than they do the external prefixes from a prospective of the administrative distance.
0:09:11	So, we can see internal EIGRP uses a distance of 90,
0:09:14	where external EIGRP uses a distance of 170.
0:09:18	So, this means that if I were learning an external OSPF route,
0:09:23	and an external EIGRP route,
0:09:25	and there are equal longest matches for the same destination,
0:09:29	I would prefer to install the OSPF route into the routing table,
0:09:33	and not the external EIGRP route.
0:09:36	And the reason why is that the external EIGRP route has the higher distance of 170 versus the 110 for OSPF.
0:09:45	Now, the reason that this could potentially be an issue
0:09:48	is that the advertisement rules for EIGRP and RIP are different than OSPF and BGP.
0:09:58	Where RIP and EIGRP, since they are distance vector protocols,
0:10:02	they can only advertise routes that are actually get installed in the routing table.
0:10:07	So, when EIGRP is generating its update messages or RIP is generating its update messages,
0:10:13	those are coming from the routes in the routing table,
0:10:16	not the routes that are installed in the routing database, or the routing topology.
0:10:22	We'll see the reason that this becomes significant
0:10:25	is that if we are learning an external EIGRP route with the distance of 170,
0:10:30	and a RIP route with a distance of 120, or an OSPF route of 110,
0:10:36	and the EIGRP route is not get installed in the routing table,
0:10:41	it implies that we cannot advertise that prefix to other EIGRP peers.
0:10:47	So, we can end up in certain redistribution designs,
0:10:50	where there's not necessarily a loop in the network
0:10:53	that's related to the metric or the administrative distance,
0:10:56	but simply, certain peers in the network will not learn about different routes
0:11:02	based on the advertisement rules of either EIGRP or RIP.
0:11:08	Now, we'll see that OSPF and BGP do not have this limitation,
0:11:12	because with OSPF, since it is a link state protocol,
0:11:16	all the routers within the link state flooding domain have to have the same copy of the database.
0:11:21	So, this means that if router 1 and router 2 are both in area zero,
0:11:26	regardless what routes router 1 is installing into its routing table,
0:11:31	it has to advertise the entire OSPF database to router 2.
0:11:35	It's then up to the routers individually
0:11:38	to figure out which routes are actually gonna go from the routing database to the routing table.
0:11:44	But with EIGPR and RIP,
0:11:46	whatever is in the routing table is gonna map one to one with what is actually being advertised.
0:11:52	Now, in the case of BGP,
0:11:54	the routes that are candidate to be installed in the routing table
0:11:57	are the ones that win the BGP best path selection process.
0:12:02	So, this could be based on the highest local preference,
0:12:06	the shorter AS path value, the lower multi-exit discriminator value.
0:12:11	So, whichever prefixes are considered the best routes in BGP,
0:12:16	those are the ones that are candidate to be installed in the routing table,
0:12:19	and also candidate to be advertised to other peers.
0:12:23	We'll see later some cases with BGP
0:12:27	that we can have a situation where the route is chosen as the best path.
0:12:33	It is not installed in the routing table,
0:12:36	but it is still advertised to other BGP peers.
0:12:39	And this is a type of case where BGP can end up in a routing loop or a traffic loop
0:12:46	if what we're installing in the routing table
0:12:48	doesn't actually match up with what's being advertised to our other peers.
0:12:54	So, the next thing we need to know
0:12:57	is what are some of the differences between the IGPs and BGPs specifically,
0:13:02	on how they treat the internal routes versus the external routes,
0:13:06	and how they do the path selection on one versus the other.
0:13:10	Now, the first and most problematic protocol we'll see here
0:13:15	is RIP version 2,
0:13:17	where it does not differentiate between and internal route in an external route.
0:13:23	So, this means that if I redistribute EIGRP into RIP,
0:13:27	when I send my RIP update out to my connected peers,
0:13:30	I'm not telling them that this route came from EIRGP domain.
0:13:34	I'm simply saying, "This is the prefix, this is the hop count."
0:13:38	There is no other information that is encoded inside the actual update message.
0:13:44	So, we'll see that we can have potential issues with RIP,
0:13:47	where it does not choose the correct path,
0:13:51	because the router cannot distinguish between what are the internal routes and what are the external routes.
0:13:56	We'll also see that for both of these type of routes, internal and external,
0:14:01	RIP is gonna treat them the same with the administrative distance of 120.
0:14:05	And there's no way that we can separate on the routing process
0:14:08	and internal RIP distance versus an external RIP distance.
0:14:15	The next important point here is that when we redistribute into RIP,
0:14:19	for example, OSPF into RIP, or EIGRP into RIP,
0:14:23	there is no default seed metric or seed hop count.
0:14:27	So, this means that we either need to specify the metric
0:14:30	globally under the process with the default metric command,
0:14:33	or specifically for that individual protocol.
0:14:37	So, we could say for example, Redistribute OSPF 1 Metric 5.
0:14:41	Redistribute EIGRP 100 Metric 3.
0:14:45	So, regardless whether we're specifying them on in the individual protocol,
0:14:49	where globally is a default for the process,
0:14:52	if we do not specify the metric,
0:14:54	the routes will not be populated into the RIP database.
0:14:58	Now, we'll also see, there's a basic verification we can do on the command line
0:15:03	to look at the Show IP RIP Database.
0:15:05	That's gonna tell us locally on the router that is doing the redistribution
0:15:09	whether the process is actually occurring properly.
0:15:13	So, if I redistribute EIGRP into RIP,
0:15:16	look at the Show IP RIP Database, and I do not see the EIGRP routes as redistributed,
0:15:21	then, I know there could be a potential issue with the metric,
0:15:24	or maybe the routes are being filtered for some reason
0:15:27	based on the manual redistribution policy that I'm defining.
0:15:33	Our next IGP we have is EIGRP,
0:15:36	which does differentiate between the internal and the external routes.
0:15:42	By default, EIGRP uses an administrative distance of 90 for the internal routes,
0:15:47	and 170 for the external routes.
0:15:50	Now, the idea behind this...
0:15:53	is that if we have an external EIGRP route and some other IGP learned prefix,
0:16:00	okay, so, for the exact same match, let's say 1.2.3.0/24.
0:16:05	If I'm learning the route through external EIGRP,
0:16:08	this is going to be the least preferred of the IGP paths.
0:16:13	So, if I have external EIGRP versus RIP,
0:16:16	external EIGRP versus OSPF, versus EBGP,
0:16:19	I would always choose the EIGRP route last.
0:16:24	We'll see that this automatic behavior
0:16:27	is gonna help to prevent some route feedback scenarios
0:16:31	where if the administrative distance was not higher for external EIGRP,
0:16:36	the router could accidentally choose the wrong path to the destination
0:16:40	based on the distance of the EIGRP.
0:16:45	But we'll see, since it does use that higher external distance by default,
0:16:49	a lot of the times, it's gonna prevent any redistribution problems we could potentially have
0:16:53	before we actually see any of the issues.
0:16:59	Now, the other important thing to note here about EIGRP
0:17:02	is that it uses the router ID value for loop prevention of external prefixes.
0:17:09	So, if my EIGRP router ID is 1.2.3.4,
0:17:13	when I redistribute OSPF into EIGRP,
0:17:18	those EIGRP external prefixes, they're gonna be tagged with my local router ID 1.2.3.4.
0:17:25	This then means that if the routing update
0:17:29	somehow leaves me and goes out to my peers,
0:17:31	and then comes back in from another EIGRP neighbor,
0:17:35	we're automatically going to discard those advertisements.
0:17:39	So, anytime you'll learn an external EIGRP route
0:17:42	that has your router ID as the originating router,
0:17:45	the process is automatically going to deny this.
0:17:50	Now, this would be the ideal default loop prevention mechanism,
0:17:54	but we could run into design cases where if two EIGRP neighbors are sharing the same router ID,
0:18:01	they would not be install each other's external routes.
0:18:06	So, basically, in that case, it's a configuration error.
0:18:10	Where you would not want EIGRP neighbors to have the same router ID,
0:18:14	because they're gonna use that for the external loop prevention mechanism.
0:18:21	Now, just like RIP,
0:18:23	EIGRP does not have a default seed metric
0:18:26	unless we're going between two separate EIGRP processes.
0:18:30	So, if I have EIGRP AS 1 and EIGRP AS 2 locally on the same router,
0:18:35	when I redistribute between the two of them,
0:18:37	the individual composite values of the route will be exchanged on a prefix-by-prefix basis.
0:18:45	So, the minimum bandwidth along the path,
0:18:48	the cumulative delay,
0:18:50	the worst load over the path, the worst reliability over the path,
0:18:56	and then the lowest MTU,
0:18:58	that would automatically be exchanged between the two processes.
0:19:03	However, anytime we're coming from another routing process like OSPF in the EIGRP,
0:19:08	or RIP in the EIGRP,
0:19:10	we do not to manually specify what the seed metric value is.
0:19:15	Now, just like RIP, we could do this globally under the process
0:19:19	with the default metric command.
0:19:21	Or we could specify it on a per-protocol basis when we're actually doing the redistribution.
0:19:27	So, we could say Redistribute OSPF 1 Metric
0:19:30	followed by the bandwidth, delay load, reliability, and MTU.
0:19:35	So, you don't necessarily need to memorize what is the order
0:19:39	for the redistribution metrics,
0:19:41	because we'll see when we look at the command line, we can simply use the question mark
0:19:44	to figure out what are the individual values that it wants.
0:19:50	Now, we'll also see in cases
0:19:52	where there are only a single point of redistribution,
0:19:56	the seed metric value whether we're going into RIP, or into EIGRP, or into OSPF,
0:20:02	the metric value is not really gonna matter.
0:20:05	Because if I'll have only one physical path...
0:20:09	from the RIP domain into the EIGRP domain,
0:20:12	it really doesn't matter what metric that EIGRP routers see for the RIP domain.
0:20:18	Regardless what that is, they're gonna have to go through
0:20:21	that single physical point that's actually doing the redistribution.
0:20:26	So, in reality, the seed metric value is only gonna matter
0:20:29	when there are multiple points of redistribution.
0:20:32	And we're trying to do some sort of traffic engineering to prefer one path over another,
0:20:38	or we're trying to prevent some sort of route feedback
0:20:42	to make sure that we prefer the correct path with the lower metric
0:20:46	over the incorrect path with the higher metric.
0:20:52	Next, we have OSPF redistribution here,
0:20:55	where although, it does distinguish between internal versus external routes,
0:21:00	all of them are gonna be assigned in an administrative distance of 110.
0:21:05	So, this means that if I am redistributing from RIP into OSPF, or EIGRP into OSPF,
0:21:10	and then I'm looking at some other path
0:21:14	whether it's IBGP learned or external EIGRP learned,
0:21:18	I would prefer the external OSPF route
0:21:21	with a lower distance of 110 versus RIP at 120, or external EIGRP at 170, or IBGP at 200.
0:21:32	We'll also see that under the...
0:21:35	the routing process on the command line,
0:21:37	we can manually specify a different administrative distance
0:21:40	for the external routes versus the internal routes if we wanted to.
0:21:46	So, we can get the same default behavior that we do in EIGRP,
0:21:50	where we could specify under the OSPF routing process
0:21:53	that I would want to prefer the internal OSPF versus the...
0:21:57	external OSPF when I'm comparing this to different protocols.
0:22:04	Now, as we talked about previously in OSPF,
0:22:08	even though the administrative distance is the same for the internal versus the external routes,
0:22:13	by default, based on the RFC of how the OSPF path selection state machine works,
0:22:19	we have to choose the intra-area routes over the inter-area routes
0:22:26	over external Type-1 over external Type-2 over N1 over N2.
0:22:32	So, this would then mean regardless of what the metric value is, or what the administrative distance is,
0:22:38	if I have an E1 versus an N1 route,
0:22:43	so N1 for not-so-stubby.
0:22:45	I would always have to choose the E1 route.
0:22:49	So, we'll see, in OSPF, really, the only time that the metric is gonna matter
0:22:53	for the redistributed routes is when we have multiple longest matches of the same external route type,
0:23:01	then, we would use the metric value to choose one versus the other.
0:23:06	So, if we have two E1 routes, I'm gonna pick whichever one has the lower metric.
0:23:11	If I have two E2 routes,
0:23:13	I'm gonna pick whichever one has the lower metric,
0:23:16	or if there is a tie in the metric,
0:23:19	I would then choose the one that has the shorter path to the ASBR.
0:23:24	So, we'll see, when we actually do the redistribution in the OSPF,
0:23:28	the external 2 and the NSSA external 2, which is N2 in the routing table,
0:23:33	those are gonna distinguish between the metric of the routes plus the forward metric
0:23:40	which is the cost to reach the ASBR.
0:23:44	Whereas the E1 and the N1 routes,
0:23:47	those are gonna take the cost that we're redistributing in.
0:23:51	So, the seed metric value simply add that to our cost of the ASBR,
0:23:55	and that's what's gonna show up in the routing table.
0:24:00	Now, OSPF does have a default seed metric of 20
0:24:04	regardless of what protocol we're coming from.
0:24:06	And we're also gonna use the default metric type of E2 into a normal area,
0:24:13	and N2 into a not-so-stubby area.
0:24:18	We could manually change both the metric and the metric type,
0:24:22	but just by default, we don't necessarily have to specify this,
0:24:25	because it does have the default value of 20 and then the default metric type of 2.
0:24:31	We'll also see that OSPF like EIGRP
0:24:35	is gonna use the router ID value to prevent any looping of the route advertisement.
0:24:41	Now, in OSPF, this isn't really a big of a deal as it is for EIGRP.
0:24:46	Because OSPF is not a distance vector protocol.
0:24:50	We're assuming that all of the routers in the area are agreeing on the topology.
0:24:55	So, they're gonna end up in the same end result for SPF.
0:25:00	Really, what we care about for looping of OSPF
0:25:04	is we wanna make sure that the LSA flooding process doesn't happen infinitely.
0:25:10	So, when I redistribute EIGRP into OSPF, or RIP into OSPF,
0:25:14	I'm gonna tag inside the external LSA,
0:25:19	so the LSA Type-5 for either the E1 or E2 routes,
0:25:24	or the LSA Type-7 for the N1 or N2 routes,
0:25:28	I'm gonna set my own router ID as the originating router.
0:25:33	So, if for some reason I flooded LSA out,
0:25:36	then, it comes back in from another neighbor,
0:25:38	I know to discard that LSA and not continue to advertise it on.
0:25:45	So, OSPF, it does not use a split horizon like behavior
0:25:49	similar to RIP or EIGRP, its gonna use the router ID in the LSA
0:25:55	to figure out if I was the person who actually originated the prefix.
0:26:00	Then, our last protocol here is BGP
0:26:03	that does distinguish between the external and the internal routes two different ways.
0:26:11	First is gonna be based on the origin code
0:26:14	that is set to incomplete or a question mark when we look at the Show IP BGP Output
0:26:20	as one of the attributes of the prefix.
0:26:24	So, when we look at the BGP best path selection order,
0:26:27	we would prefer the routes that are internal to the network.
0:26:32	So, that actually came from the network statement on to the BGP process
0:26:35	versus the ones that are redistributed.
0:26:38	So, we see the origin code for the internal routes as a lower case "i"
0:26:43	versus the question mark for incomplete.
0:26:46	So, if we have two routes that have every other attribute being equal,
0:26:51	the weight, the local preference, the AS path, the med value,
0:26:54	then, we're gonna look at the origin code,
0:26:56	and prefer the one that has the lower origin code,
0:27:00	where IGP is preferred over incomplete.
0:27:06	Now, for the loop prevention of the external routes,
0:27:10	we're gonna use the same underlying advertisement rules that we do for normal EBGP and normal IBGP,
0:27:16	where EBGP, we use the AS path information
0:27:20	that if my AS is 100,
0:27:22	and I received a route in that has 100 in the path,
0:27:25	then, I'm simply going to discard that update.
0:27:28	Whereas with IBGP routes,
0:27:31	anytime I learn a prefix from an IBGP neighbor,
0:27:34	I'm simply not going to advertise it to other IBGP neighbors unless I am a route reflector.
0:27:43	So, we can assume that if the normal BGP advertisements are loop-free to begin with,
0:27:47	then, we don't really need to distinguish between the internal loop prevention versus the external loop prevention.
0:27:55	Now, we'll also see that there are some differences
0:27:58	when we're redistributing from IGP into BGP
0:28:02	versus redistributing BGP into IGP.
0:28:07	Now, the first one, IGP to BGP, this would be one of the normal ways
0:28:13	that we advertise our internal prefixes out to the global BGP network.
0:28:19	So, if I have a bunch of OSPF learned routes that I wanna advertise into BGP,
0:28:23	I could either use the network statement under the process,
0:28:26	or I could just redistribute OSPF into BGP.
0:28:31	The only exception for this
0:28:33	is that by default, the BGP process is going to deny the external OSPF routes.
0:28:42	So, the logic behind this is that if the route is external OSPF,
0:28:47	it means that it came from some other protocol that was not OSPF to begin with.
0:28:52	So, by filtering those out by default,
0:28:55	we would prevent the case that we redistribute from BGP to OSPF,
0:28:59	from OSPF back into BGP,
0:29:02	and then, we cause a routing loop in the advertisement.
0:29:06	Now, in topologies that we can guarantee that a loop will not occur,
0:29:11	we can manually tell the process to include the external routes
0:29:15	if we say Match Internal External at the end of the redistribute OSPF statement.
0:29:23	So, the key point being here is that this only applies to OSPF.
0:29:27	If we were to redistribute EIGRP into BGP,
0:29:30	it's gonna allow both the internal routes and the external routes to go.
0:29:36	Now, on the other way back, as we're going from BGP to IGP,
0:29:41	in order to prevent loops inside of our own internal BGP network,
0:29:46	we're only going to allow external routes to go from BGP to OSPF, or from BGP to EIGRP.
0:29:55	So, the internal BGP routes, those are going to be denied by default.
0:29:58	We can override this with the BGP redistribute internal command.
0:30:04	But the vast majority of the time, you would not wanna do this.
0:30:08	So, it's very easy to cost a traffic loop inside of the IGP domain,
0:30:13	because of the administrative distance of IBGP versus IGP.
0:30:21	So, if we look back at our administrative distance table,
0:30:24	note that external BGP...
0:30:26	is the most preferred of the dynamic protocols.
0:30:31	Now, technically, we have the EIGRP summary with the distance of 5,
0:30:35	but that would be a locally generated summary.
0:30:38	So, most of the time, we're not gonna have other matches that are equal to the EIGRP summary.
0:30:44	So, for actual dynamically learned information, EBGP is gonna be the lowest.
0:30:49	Then, on the other end of the spectrum,
0:30:51	the least preferred dynamic protocol is internal BGP.
0:30:57	So, this then means, if I have an IBGP route that has a distance of 200,
0:31:03	and I redistribute it into IGP.
0:31:06	So, it doesn't matter what protocol, BGP to OSPF, BGP to RIP, BGP to EIGRP or IS-IS.
0:31:14	Once I do that internal BGP to IGP redistribution,
0:31:20	I would always prefer the IGP route over the internal BGP route.
0:31:28	So, it's basically gonna invalidate where the BGP information came from.
0:31:33	So, the potential case that we could run into where this would be a problem
0:31:38	is let's say that between router 4,
0:31:42	and the backbone router we're running BGP here.
0:31:46	Let's say router 4 is AS 1, and BB3 is AS 2.
0:31:52	Okay, we have...
0:31:54	EBGP learned routes coming in here.
0:31:57	And then, router 4 is advertising them let's say to router 1.
0:32:03	Okay, router 1's also in AS 1.
0:32:05	So this is an IBGP peering.
0:32:09	Now, we would assume that internal to our network, if router 1 and router 4 are both in AS 1,
0:32:17	they're most likely sharing an IGP.
0:32:19	So, maybe they're running OSPF on this link, or they're running EIGRP,
0:32:25	or they're running IS-IS.
0:32:29	If on router 1, we were to redistribute from BGP back into IGP,
0:32:36	and we were to allow the IBGP learned routes to be redistributed,
0:32:41	router 4 would then be learning the IBGP,
0:32:45	actually not the IBGP, it's learning the EBGP route with the distance of 20.
0:32:51	Then the IBGP route where IS-IS would be 115,
0:32:55	EIGRP would be 170, OSPF is gonna be 110.
0:33:00	Okay, so this is not necessarily a problem.
0:33:02	Where the issue comes in
0:33:05	is that when there's someone else in the transit path,
0:33:09	let's say between router 4 and router 1,
0:33:15	where we have...
0:33:26	we have AS 2 on BB3.
0:33:28	And then let's say our whole entire network here AS 1.
0:33:33	So, router 4 is peering with BB3, we're learning EBGP routes here.
0:33:39	Router 1 sends this route to...
0:33:42	Or router 4 send this route to router 1.
0:33:44	Let's say router 1 is a route reflector,
0:33:46	and then it sends it down to other peers. Let's say to router 3.
0:33:51	So, from router 3's perspective, we're learning this through IBGP.
0:33:57	From router 1's perspective, it is learning this from IBGP.
0:34:01	Now, let's say we're doing the redistribution from IBGP to IGP on router 3.
0:34:09	So, 3 takes the BGP learned route,
0:34:12	and it send it in to OSPF.
0:34:16	If somehow router 1 learns this prefix back through IGP,
0:34:22	it's now gonna have a distance through OSPF or 110,
0:34:28	and the IBGP distance of 200,
0:34:31	which means we would prefer the IGP route,
0:34:35	and then eventually route the traffic in the wrong direction.
0:34:40	So, we'll see, this is one of the common design problems that we're gonna look at today when we're doing redistribution.
0:34:46	If the router is choosing the wrong path based on the distance,
0:34:51	then, we could potentially end up in route feedback
0:34:55	where the route is being installed in the routing table,
0:34:58	and then delete it from the routing table over and over and over,
0:35:01	or we could end up in a loop in the data plane
0:35:05	where the route is installed in the table and is stable.
0:35:09	So the route is not flapping in and out or flapping in between protocols,
0:35:13	but it's simply installed via the wrong information.
0:35:17	So, we'll see, the difference between those
0:35:20	is the one that is flapping between the protocols,
0:35:24	a lot of the times, that's real easy to see if we look at stuff like Debug IP Routing,
0:35:28	or we look at the IP Route Profile.
0:35:31	But the prefix that is installed based on the wrong metric value,
0:35:35	or simply the wrong path is installed, but it's stable,
0:35:41	we would see, that would end up in traffic being routed in the wrong direction.

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The CCIE Routing & Switching Advanced Technologies Class is the first step in understanding CCIE level technologies and is a companion to the Advanced Technologies Lab Workbook. Each technology you need to know for the CCIE Routing & Switching lab will be described in detail using an instructor led hands on demonstration. The class consists of over 80 hours of in depth explanations and examples.
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Route Redistribution Overview

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