From: Hunt Lee (ciscoforme3@xxxxxxxxxxxx)
Date: Wed Jul 24 2002 - 11:48:31 GMT-3
Can someone please clarify this for me?
RTB
/
RTD -- RTA
\
RTC
RTB & RTC are both in AS1
RTA & RTD are both in AS2
RTD's interface (connecting to RTA) :- 25.25.25.1
RTA's interface (back to RTD) :- 25.25.25.2
RTA's interface (to RTB) :- 10.1.1.1
RTB's interface (back to RTA) :- 10.1.1.2
RTA's interface (to RTC) :- 10.1.2.1
RTC's interface (back to RTA) :- 10.1.2.2
RTA is connected with RTB & C with Serial connections, while
connecting with RTD with Ethernet
Both RTB & RTC are advertising a network 172.17.1.0/24 (directly
connected via Eth from both routers). Also, in order to do BGP load
balancing to that network, I have use the "maximum-paths 6" command
at RTA.
RouterA#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
172.17.0.0/24 is subnetted, 1 subnets
B 172.17.1.0 [20/0] via 10.1.2.2, 00:36:24
[20/0] via 10.1.1.2, 00:36:18
25.0.0.0/24 is subnetted, 1 subnets
C 25.25.25.0 is directly connected, Ethernet0
10.0.0.0/30 is subnetted, 2 subnets
C 10.1.2.0 is directly connected, Serial1
C 10.1.1.0 is directly connected, Serial0
RouterA#
Ok, here's what I am very confused. When I lookup RTD's BGP table
(shown below), for the BGP route 172.17.1.0/24, instead of the
Next-hop being 10.1.1.2 or 10.1.2.2, it is 25.25.25.2. Since I
thought that in EBGP peering, the next hop is the IP address of the
neighbor that announced the route, while IBGP peering preserve the
Next-hop attribute learned from EBGP peers. So in the case, if I
haven't use next-hop-self on RTA, I would think the Next-Hop in RTD's
BGP table would be either 10.1.1.2 or 10.1.2.2....
RouterD#sh ip bgp
BGP table version is 9, local router ID is 25.25.25.1
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
*>i10.1.1.0/30 25.25.25.2 100 0 1 i
*>i10.1.2.0/30 25.25.25.2 100 0 1 i
*>i25.25.25.0/24 25.25.25.2 0 100 0 i
*>i172.17.1.0/24 25.25.25.2 0 100 0 1 i
RouterD#
RouterA#sh ip bgp
BGP table version is 12, local router ID is 25.25.25.2
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
*> 10.1.1.0/30 10.1.2.2 0 1 i
* 10.1.1.2 0 0 1 i
*> 10.1.2.0/30 10.1.1.2 0 1 i
* 10.1.2.2 0 0 1 i
*> 25.25.25.0/24 0.0.0.0 0 32768 i
*> 172.17.1.0/24 10.1.1.2 0 0 1 i
* 10.1.2.2 0 0 1 i
RouterA#
RouterB#sh ip bgp
BGP table version is 7, local router ID is 172.17.1.1
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
*> 10.1.1.0/30 0.0.0.0 0 32768 i
*>i10.1.2.0/30 172.17.1.2 0 100 0 i
* i25.25.25.0/24 10.1.2.1 0 100 0 2 i
*> 10.1.1.1 0 0 2 i
* i172.17.1.0/24 172.17.1.2 0 100 0 i
*> 0.0.0.0 0 32768 i
RouterB#
RouterC#sh ip bgp
BGP table version is 7, local router ID is 172.17.1.2
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
*>i10.1.1.0/30 172.17.1.1 0 100 0 i
*> 10.1.2.0/30 0.0.0.0 0 32768 i
* i25.25.25.0/24 10.1.1.1 0 100 0 2 i
*> 10.1.2.1 0 0 2 i
* i172.17.1.0/24 172.17.1.1 0 100 0 i
*> 0.0.0.0 0 32768 i
RouterC#
Thanks
Hunt Lee
http://www.sold.com.au - SOLD.com.au
- Find yourself a bargain!
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