From: trouse@cisco.com
Date: Mon Oct 27 2003 - 13:48:40 GMT-3
Hi group study, this is my first post. Thanks in advance for help.
i have a problem that I dont quite understand. Can you help. I was trying to influence path selection using local preference. So on configure on of the IBGP peers (router rC) to modify local preference for routes coming in from AS100 into AS200. AS200 is multi homed b/c rB also has a EBGP peer to AS100 also (same EBGP peer as rC). The problem is rB is seeing the local-preference change but is not making it the preferred route ( thru AS200/rC). By trial and error I figure out that turning off synchronization on rB fixes this problem but I dont understand why. There IGPs was synchronized and the next hop (193.1.1.0) was in rB routing table. how would I identify this little issue in the real lab. All routes work, but patch selection is not as expected. Do you normally do trace routes for all routes or what? I guess it would not hurt for verification. I probably would have taken it for granted thought. All was find on Router D ( the other IBGP peer) because I initia!
lly had synchronization off. BTW, the 3 IBGP peers are fully meshed as well. BTW this scenario comes form "All-in-one CCIE Lab Study Guide" Lab #34 P.545
Thanks again.
Router C config:
=================
interface Ethernet0
description EBGP connection to AS100
ip address 193.1.1.2 255.255.255.0
!
interface Serial0
ip address 195.1.1.2 255.255.255.0
clockrate 64000
!
interface Serial1
no ip address
!
router ospf 64
log-adjacency-changes
passive-interface Ethernet0
network 193.0.0.0 0.255.255.255 area 0
network 195.0.0.0 0.255.255.255 area 0
!
router bgp 200
no synchronization
bgp log-neighbor-changes
neighbor 193.1.1.1 remote-as 100
neighbor 193.1.1.1 route-map localpref in
neighbor 194.1.1.2 remote-as 200
neighbor 195.1.1.1 remote-as 200
!
ip classless
no ip http server
!
access-list 1 permit 1.0.0.0 0.255.255.255 log
route-map localpref permit 10
match ip address 1
set local-preference 200
!
route-map localpref permit 20
set local-preference 100
I can ping both of router C interfaces from Router B
====================================================
rB#ping 195.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 195.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/37/48 ms
rB#ping 193.1.1.2
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 193.1.1.2, timeout is 2 seconds:
!!!!!
Success rate is 100 percent (5/5), round-trip min/avg/max = 32/32/36 ms
rB#rB#ping 193.1.1.1
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 193.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
I realize not being able to ping 193.1.1.1 may be a problem but why does it work when sychronizatoin is OFF.
Router B's config
===================
interface Ethernet0
ip address 194.1.1.2 255.255.255.0
!
interface Serial1
ip address 192.1.1.2 255.255.255.0
!
router ospf 64
log-adjacency-changes
network 0.0.0.0 255.255.255.255 area 0
!
router bgp 200
bgp log-neighbor-changes
neighbor 192.1.1.1 remote-as 100
neighbor 194.1.1.1 remote-as 200
neighbor 195.1.1.2 remote-as 200
rB#sh ip bgp
BGP table version is 3, local router ID is 194.1.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
*> 1.0.0.0 192.1.1.1 0 0 100 i
* i 193.1.1.1 0 200 0 100 i
*> 2.0.0.0 192.1.1.1 0 0 100 i
* i 193.1.1.1 0 100 0 100 i
I know I am not reading these "i" correctly, and I am missing something here. That may be the problem.....
Router D is okay in comparison
rD#sh ip bgp
BGP table version is 47, local router ID is 200.0.0.1
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i1.0.0.0 192.1.1.1 0 100 0 100 i
*>i 193.1.1.1 0 200 0 100 i
*>i2.0.0.0 192.1.1.1 0 100 0 100 i
* i 193.1.1.1 0 100 0 100 i
rB#sh ip route
Gateway of last resort is not set
B 1.0.0.0/8 [20/0] via 192.1.1.1, 18:16:19
B 2.0.0.0/8 [20/0] via 192.1.1.1, 18:16:19
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/11] via 194.1.1.1, 22:29:43, Ethernet0
O 193.1.1.0/24 [110/84] via 194.1.1.1, 22:29:43, Ethernet0
C 192.1.1.0/24 is directly connected, Serial1
O 195.1.1.0/24 [110/74] via 194.1.1.1, 22:29:43, Ethernet0
C 194.1.1.0/24 is directly connected, Ethernet0
rB#sh ip rout bgp
B 1.0.0.0/8 [20/0] via 192.1.1.1, 18:16:26
B 2.0.0.0/8 [20/0] via 192.1.1.1, 18:16:26
rB#sh ip bgp summary
BGP router identifier 194.1.1.2, local AS number 200
BGP table version is 3, main routing table version 3
2 network entries and 4 paths using 338 bytes of memory
3 BGP path attribute entries using 180 bytes of memory
1 BGP AS-PATH entries using 24 bytes of memory
0 BGP route-map cache entries using 0 bytes of memory
0 BGP filter-list cache entries using 0 bytes of memory
BGP activity 18/208 prefixes, 31/27 paths, scan interval 60 secs
Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
192.1.1.1 4 100 2787 2785 3 0 0 18:34:22 2
194.1.1.1 4 200 1392 1397 3 0 0 18:34:33 0
195.1.1.2 4 200 1393 1388 3 0 0 18:34:33 2
sho ip bgp neighbors
BGP neighbor is 192.1.1.1, remote AS 100, external link
BGP version 4, remote router ID 192.1.25.1
BGP state = Established, up for 18:35:00
Last read 00:00:00, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
BGP neighbor is 194.1.1.1, remote AS 200, internal link
BGP version 4, remote router ID 200.0.0.1
BGP state = Established, up for 18:35:39
Last read 00:00:40, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
BGP neighbor is 195.1.1.2, remote AS 200, internal link
BGP version 4, remote router ID 192.168.4.1
BGP state = Established, up for 18:35:54
Last read 00:00:53, hold time is 180, keepalive interval is 60 seconds
Neighbor capabilities:
Route refresh: advertised and received(new)
Address family IPv4 Unicast: advertised and received
Received 1394 messages, 0 notifications, 0 in queue
Solutions tried.
I tied change the next-hop advertised by router C but that did not help.
rC#conf t
Enter configuration commands, one per line. End with CNTL/Z.
rC(config)#router bgp 200
rC(config-router)#neighbor 194.1.1.2 next-hop-self
rC(config-router)#^Z
rC#clear ip bgp 194.1.1.2
rC#
2w1d: %BGP-5-ADJCHANGE: neig
TS1#1
[Resuming connection 1 to r2 ... ]
rB#sh ip bgp
BGP table version is 3, local router ID is 194.1.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i1.0.0.0 195.1.1.2 0 200 0 100 i
*> 192.1.1.1 0 0 100 i
* i2.0.0.0 195.1.1.2 0 100 0 100 i
*> 192.1.1.1 0 0 100 i
WORKING SOLUTION---- TURN Synchronization OFF:
rB#conf t
Enter configuration commands, one per line. End with CNTL/Z.
rB(config)#router bgp 200
rB(config-router)#no sync
rB(config-router)#no synchronization
rB(config-router)#^Z
rB#sh ip
5d17h: %SYS-5-CONFIG_I: Configured from console by console
rB#sh ip bg
rB#sh ip bgp
BGP table version is 3, local router ID is 194.1.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* i1.0.0.0 193.1.1.1 0 200 0 100 i
*> 192.1.1.1 0 0 100 i
* i2.0.0.0 193.1.1.1 0 100 0 100 i
*> 192.1.1.1 0 0 100 i
rB#clear ip bg
rB#clear ip bgp *
rB#
5d17h: %BGP-5-ADJCHANGE: neighbor 192.1.1.1 Down User reset
5d17h: %BGP-5-ADJCHANGE: neighbor 194.1.1.1 Down User reset
5d17h: %BGP-5-ADJCHANGE: neighbor 195.1.1.2 Down User reset
rB#
5d17h: %BGP-5-ADJCHANGE: neighbor 194.1.1.1 Up
rB#
5d17h: %BGP-5-ADJCHANGE: neighbor 195.1.1.2 Up
rB#
5d17h: %BGP-5-ADJCHANGE: neighbor 192.1.1.1 Up
rB#sh ip bgp
BGP table version is 3, local router ID is 194.1.1.2
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal
Origin codes: i - IGP, e - EGP, ? - incomplete
Network Next Hop Metric LocPrf Weight Path
* 1.0.0.0 192.1.1.1 0 0 100 i
*>i 193.1.1.1 0 200 0 100 i
*> 2.0.0.0 192.1.1.1 0 0 100 i
* i 193.1.1.1 0 100 0 100 i
rB#ping 193.1.1.1 <--still not reachable
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 193.1.1.1, timeout is 2 seconds:
.....
Success rate is 0 percent (0/5)
rB#sh ip route
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
B 1.0.0.0/8 [200/0] via 193.1.1.1, 00:01:26
B 2.0.0.0/8 [20/0] via 192.1.1.1, 00:01:26
4.0.0.0/32 is subnetted, 1 subnets
O 4.4.4.4 [110/11] via 194.1.1.1, 23:24:34, Ethernet0
O 193.1.1.0/24 [110/84] via 194.1.1.1, 23:24:34, Ethernet0
C 192.1.1.0/24 is directly connected, Serial1
O 195.1.1.0/24 [110/74] via 194.1.1.1, 23:24:34, Ethernet0
C 194.1.1.0/24 is directly connected, Ethernet0
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