R1－－－(R2－－－R3－－－R4)－－R5
|__EBGP__|_____IBGP______|__EBGP_|
12.0/24 23.0/24 34.0/24 45.0/24
R2-R4 is the MPLS domain
Redistribute directly to interfaces to EBGP neighbors on R2 and R4
Use loopback1 on R1 and R5 as internet route
r1#sh ip b
BGP table version is 7, local router ID is 1.1.1.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 11.11.11.11/32 0.0.0.0 0 32768 i
*> 55.55.55.55/32 192.168.12.2 0 1 3 i
*> 192.168.12.0 192.168.12.2 0 0 1 ?
*> 192.168.45.0 192.168.12.2 0 1 ?
r5#sh ip b
BGP table version is 7, local router ID is 5.5.5.5
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 11.11.11.11/32 192.168.45.4 0 1 2 i
*> 55.55.55.55/32 0.0.0.0 0 32768 i
*> 192.168.12.0 192.168.45.4 0 1 ?
*> 192.168.45.0 192.168.45.4 0 0 1 ?
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r2# sh ip b
BGP table version is 5, local router ID is 2.2.2.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
r RIB-failure
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 11.11.11.11/32 192.168.12.1 0 0 2 i
*>i55.55.55.55/32 192.168.45.5 0 100 0 3 i
*> 192.168.12.0 0.0.0.0 0 32768 ?
*>i192.168.45.0 4.4.4.4 0 100 0 ?
r2#sh ip route
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/129] via 192.168.23.3, 01:26:32, Serial2/0
r2 searched the routing table and found that i55.55.55.55/32 is a bgp route, and mpls will not assign tags to routes received from bgp. It searched again and found that the next hop address of i55.55.55/32 is 192.168.45.5. Similarly, looking up the routing table again and finally found that 4.4.4.4 is an IGP route. R3 assigned a 301 tag to R2 to 4.4.4.4.4. At this time, the most shameless thing happened. R2 copied this tag to the CEF table about 55.55.55.55 and 192.168.45.0/24, and pushed into the tag, that is, all bgp routes received from 192.168.45.5 have this behavior, as shown below:
r2#show ip cef detail
4.4.4.4/32, version 10, epoch 0, cached adjacency to Serial2/0
0 packets, 0 bytes
tag informationset, shared
local tag: 201
fast tag rewrite with Se2/0, point2point, tags imposed: {301}
via 192.168.23.3, Serial2/0, 1 dependency
next hop 192.168.23.3, Serial2/0
valid cached adjacency
tag rewrite with Se2/0, point2point, tags imposed: {301}
55.55.55.55/32, version 19, epoch 0, cached adjacency to Serial2/0
0 packets, 0 bytes
tag information from 4.4.4.4/32, shared
local tag: 201
fast tag rewrite with Se2/0, point2point, tags imposed: {301}
via 192.168.45.5, 0 dependencies, recursive
next hop 192.168.23.3, Serial2/0 via 192.168.45.0/24
valid cached adjacency
tag rewrite with Se2/0, point2point, tags imposed: {301}
192.168.45.0/24, version 18, epoch 0, cached adjacency to Serial2/0
0 packets, 0 bytes
tag information from 4.4.4.4/32, shared
local tag: 201
fast tag rewrite with Se2/0, point2point, tags imposed: {301}
via 4.4.4.4, 1 dependency, recursive
next hop 192.168.23.3, Serial2/0 via 4.4.4.4/32
valid cached adjacency
tag rewrite with Se2/0, point2point, tags imposed: {301}
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The router will not assign tags to routes received from bgp, so you can't see the tag bindings for 55.55.55.55/32 here
r2#sho tag tdp bind
tib entry: 2.2.2.2/32, rev 4
local binding: tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: 300
tib entry: 3.3.3.3/32, rev 6
local binding: tag: 200
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 4.4.4.4/32, rev 8
local binding: tag: 201
remote binding: tsr: 3.3.3.3:0, tag: 301
tib entry: 192.168.12.0/24, rev 2
local binding: tag: imp-null
tib entry: 192.168.23.0/24, rev 10
local binding: tag: imp-null
remote binding: tsr: 3.3.3.3:0, tag: imp-null
tib entry: 192.168.34.0/24, rev 12
local binding: tag: 202
remote binding: tsr: 3.3.3.3:0, tag: imp-null
When R3 receives the mpls packet with 301 tag, it will bounce the last jump according to its tag forwarding table. The next jump is 4.4.4.4/32, and 4.4.4.4/32 already has internet routes, so it can forward normally
r3#show tag-switching forwarding-table
Local Outgoing Prefix Bytes tag Outgoing Next Hop
tag tag or VC or Tunnel Id switched interface
300 Pop tag 2.2.2.2/32 4061 Se2/0 point2point
301 Pop tag 4.4.4.4/32 4457 Se1/0 point2point
At this time, there is no 55.55.55.55/32 route on R3.
r3#sh ip rou
Codes: C - connected, S - static, I - IGRP, R - RIP, M - mobile, B - BGP
D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
E1 - OSPF external type 1, E2 - OSPF external type 2, E - EGP
i - IS-IS, L1 - IS-IS level-1, L2 - IS-IS level-2, ia - IS-IS inter area
* - candidate default, U - per-user static route, o - ODR
P - periodic downloaded static route
Gateway of last resort is not set
2.0.0.0/32 is subnetted, 1 subnets
O 2.2.2.2 [110/65] via 192.168.23.2, 00:28:23, Serial2/0
3.0.0.0/32 is subnetted, 1 subnets
C 3.3.3.3 is directly connected, Loopback0
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/65] via 192.168.34.4, 00:28:23, Serial1/0
C 192.168.23.0/24 is directly connected, Serial2/0
C 192.168.34.0/24 is directly connected, Serial1/0
This is to use mpls to avoid the routing black hole problem of bgp. It should be made clear? ^_^
Article entry: csh Editor in charge: csh