From: Jeff Lodwick (climberartist@xxxxxxxxxxx)
Date: Sun Nov 11 2001 - 12:41:46 GMT-3
That was something that I wasn't sure about. In the past I've only used
MED's for EBGP connections but in this scenario I wanted to try it with IBGP
connections to test out BGP's path selection. When I look in the BGP table
it shows the MED's on the routes I specified so that's why I figured it was
working but it seems like there is something else that is affecting these
routes. Below shows the routes in r1. I did a sh ip bgp before the routes
from r2 were withdrawn to show they are installed in the bgp table with the
correct metrics then removed and routes to r5 are installed with the correct
metrics but the route to 10.1.1.0 still shows with the next hop to r5 even
though it's metric/med is higher then r2. Any ideas?
r1#debug ip bgp update
BGP updates debugging is on
r1#clear ip bgp *
r1#
04:20:24: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Down User reset
04:20:24: %BGP-5-ADJCHANGE: neighbor 5.5.5.5 Down User reset
04:20:53: %BGP-5-ADJCHANGE: neighbor 2.2.2.2 Up
04:20:53: BGP(0): 2.2.2.2 computing updates, afi 0, neighbor version 0,
table version 1, starting at 0.0.0.0
04:20:53: BGP(0): 2.2.2.2 update run completed, afi 0, ran for 0ms, neighbor
version 0, start version 1, throttled to 1
04:20:53: BGP: 2.2.2.2 initial update completed
04:20:53: BGP(0): 2.2.2.2 rcvd UPDATE w/ attr: nexthop 2.2.2.2, origin i,
localpref 100, path 300 400 400
04:20:53: BGP(0): 2.2.2.2 rcvd 10.1.1.0/24
04:20:53: BGP(0): 2.2.2.2 rcvd 10.2.2.0/24
04:20:53: BGP(0): 2.2.2.2 rcvd UPDATE w/ attr: nexthop 2.2.2.2, origin ?,
localpref 100, path 300 400 400
04:20:53: BGP(0): 2.2.2.2 rcvd 137.5.0.0/24
04:20:53: BGP(0): 2.2.2.2 rcvd 137.20.103.0/24
04:20:53: BGP(0): Revise route installing 10.1.1.0/24 -> 2.2.2.2 to main IP
table
04:20:53: BGP(0): Revise route installing 10.2.2.0/24 -> 2.2.2.2 to main IP
table
04:20:53: BGP(0): Revise route installing 137.5.0.0/24 -> 2.2.2.2 to main IP
table
04:20:53: BGP(0): Revise route installing 137.20.103.0/24 -> 2.2.2.2 to main
IP tablesh ip bgp
04:20:58: BGP(0): 2.2.2.2 computing updates, afi 0, neighbor version 1,
table version 5, starting at 0.0.0.0
04:20:58: BGP(0): 2.2.2.2 update run completed, afi 0, ran for 0ms, neighbor
version 1, start version 5, throttled to 5
BGP table version is 5, local router ID is 137.20.1.33
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
*>i10.1.1.0/24 2.2.2.2 10 100 0 300 400 400 i
*>i10.2.2.0/24 2.2.2.2 20 100 0 300 400 400 i
*>i137.5.0.0/24 2.2.2.2 20 100 0 300 400 400 ?
*>i137.20.103.0/24 2.2.2.2 20 100 0 300 400 400 ?
r1#
04:21:09: %BGP-5-ADJCHANGE: neighbor 5.5.5.5 Up
04:21:09: BGP(0): 5.5.5.5 computing updates, afi 0, neighbor version 0,
table version 5, starting at 0.0.0.0
04:21:09: BGP(0): 5.5.5.5 NEXT_HOP part 1 net 10.1.1.0/24, next 2.2.2.2
04:21:09: BGP(0): 5.5.5.5 send UPDATE (format) 10.1.1.0/24, next 2.2.2.2,
metric 10, path 300 400 400
04:21:09: BGP(0): 5.5.5.5 NEXT_HOP part 1 net 10.2.2.0/24, next 2.2.2.2
04:21:09: BGP(0): 5.5.5.5 send UPDATE (format) 10.2.2.0/24, next 2.2.2.2,
metric 20, path 300 400 400
04:21:09: BGP(0): 5.5.5.5 NEXT_HOP part 1 net 137.5.0.0/24, next 2.2.2.2
04:21:09: BGP(0): 5.5.5.5 send UPDATE (format) 137.5.0.0/24, next 2.2.2.2,
metric 20, path 300 400 400
04:21:09: BGP(0): 5.5.5.5 NEXT_HOP part 1 net 137.20.103.0/24, next 2.2.2.2
04:21:09: BGP(0): 5.5.5.5 send UPDATE (format) 137.20.103.0/24, next
2.2.2.2, metric 20, path 300 400 400
04:21:09: BGP(0): 5.5.5.5 4 updates enqueued (average=67, maximum=67)
04:21:09: BGP(0): 5.5.5.5 update run completed, afi 0, ran for 4ms, neighbor
version 0, start version 5, throttled to 5
04:21:09: BGP: 5.5.5.5 initial update completed
04:21:09: BGP(0): 5.5.5.5 rcvd UPDATE w/ attr: nexthop 5.5.5.5, origin i,
localpref 100, path (65000) 600 400
04:21:09: BGP(0): 5.5.5.5 rcvd 10.1.1.0/24
04:21:09: BGP(0): 5.5.5.5 rcvd 10.2.2.0/24
04:21:09: BGP(0): 5.5.5.5 rcvd UPDATE w/ attr: nexthop 5.5.5.5, origin ?,
localpref 100, path (65000) 600 400
04:21:09: BGP(0): 5.5.5.5 rcvd 137.5.0.0/24
04:21:09: BGP(0): 5.5.5.5 rcvd 137.20.103.0/24
04:21:09: BGP(0): Revise route installing 10.1.1.0/24 -> 5.5.5.5 to main IP
table
04:21:09: BGP(0): Revise route installing 10.2.2.0/24 -> 5.5.5.5 to main IP
table
04:21:09: BGP(0): Revise route installing 137.5.0.0/24 -> 5.5.5.5 to main IP
table
04:21:09: BGP(0): Revise route installing 137.20.103.0/24 -> 5.5.5.5 to main
IP table
04:21:09: BGP(0): 2.2.2.2 computing updates, afi 0, neighbor version 5,
table version 9, starting at 0.0.0.0
04:21:09: BGP(0): 2.2.2.2 NEXT_HOP part 1 net 10.1.1.0/24, next 5.5.5.5
04:21:09: BGP(0): 2.2.2.2 send UPDATE (format) 10.1.1.0/24, next 5.5.5.5,
metric 20, path (65000) 600 400
04:21:09: BGP(0): 2.2.2.2 NEXT_HOP part 1 net 10.2.2.0/24, next 5.5.5.5
04:21:09: BGP(0): 2.2.2.2 send UPDATE (format) 10.2.2.0/24, next 5.5.5.5,
metric 10, path (65000) 600 400
04:21:09: BGP(0): 2.2.2.2 NEXT_HOP part 1 net 137.5.0.0/24, next 5.5.5.5
04:21:09: BGP(0): 2.2.2.2 send UPDATE (format) 137.5.0.0/24, next 5.5.5.5,
metric 20, path (65000) 600 400
04:21:09: BGP(0): 2.2.2.2 NEXT_HOP part 1 net 137.20.103.0/24, next 5.5.5.5
04:21:09: BGP(0): 2.2.2.2 send UPDATE (prepend, chgflags: 0x208)
137.20.103.0/24, next 5.5.5.5, metric 20, path (65000) 600 400
04:21:09: BGP(0): 2.2.2.2 3 updates enqueued (average=66, maximum=69)
04:21:09: BGP(0): 2.2.2.2 update run completed, afi 0, ran for 4ms, neighbor
version 5, start version 9, throttled to 9
04:21:10: BGP(0): 2.2.2.2 rcv UPDATE about 10.1.1.0/24 -- withdrawn
04:21:10: BGP(0): 2.2.2.2 rcv UPDATE about 10.2.2.0/24 -- withdrawn
04:21:10: BGP(0): 2.2.2.2 rcv UPDATE about 137.5.0.0/24 -- withdrawn
04:21:10: BGP(0): 2.2.2.2 rcv UPDATE about 137.20.103.0/24 -- withdrawn
04:21:39: BGP(0): 5.5.5.5 computing updates, afi 0, neighbor version 5,
table version 9, starting at 0.0.0.0
04:21:39: BGP(0): 5.5.5.5 send unreachable 10.1.1.0/24
04:21:39: BGP(0): 5.5.5.5 send UPDATE 10.1.1.0/24 -- unreachable
04:21:39: BGP(0): 5.5.5.5 send UPDATE 10.2.2.0/24 -- unreachable
04:21:39: BGP(0): 5.5.5.5 send UPDATE 137.5.0.0/24 -- unreachable
04:21:39: BGP(0): 5.5.5.5 send UPDATE 137.20.103.0/24 -- unreachable
04:21:39: BGP(0): 5.5.5.5 1 updates enqueued (average=39, maximum=39)
04:21:39: BGP(0): 5.5.5.5 update run completed, afi 0, ran for 0ms, neighbor
version 5, start version 9, throttled to 9
r1#sh ip bgp
BGP table version is 9, local router ID is 137.20.1.33
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
*> 10.1.1.0/24 5.5.5.5 20 100 0 (65000) 600 400
i
*> 10.2.2.0/24 5.5.5.5 10 100 0 (65000) 600 400
i
*> 137.5.0.0/24 5.5.5.5 20 100 0 (65000) 600 400
?
*> 137.20.103.0/24 5.5.5.5 20 100 0 (65000) 600 400
?
Thanks in advance,
Jeff
>From: "lalal" <lalal@163.com>
>To: "Jeff Lodwick" <climberartist@hotmail.com>
>Subject: Re: BGP path selection question
>Date: Sun, 11 Nov 2001 16:50:35 +0800 (CST)
>
>i think MED is used in eBGP connection.iBGP just pass it through the as,and
>so is confederation.
>
> > Hi group,
> > I added a post with the subject "Weird BGP problem/question on BGP path
> > selection" that ended up being too long after I replied a couple times
>to
> > Eric on the list because of all the configs and debug I included. If
>you
> > would like the configs they are in the post with the subject "Weird BGP
> > problem/question on BGP path selection" or I can send them again if
>someone
> > needs them. My problem in a nutshell is with how BGP's path selection
>is
> > working on this lab setup I have. I have 6 routers that all are running
> > OSPF and no virtual-link problems so that I have simple routes to all
> > subnets. The only interfaces that aren't in OSPF are 2 loopback
>interfaces
> > off r4 (10.1.1.0 and 10.2.2.0) which I have redistributed into BGP
> > redistribute connected) and advertised through BGP. I have communities
> > sending med's to r4 so that
> > r4 selects certain routes to get to 2 different subnets off r1 and it is
> > working great. R1, r2 and r5 are all in AS 100 with 2 different
> > confederation AS's (65000 on r5 and 65001 on r1 and r2). R1 has a
>neighbor
> > to r2 and r5. R2 has a neighbor to r3 in AS 300 and r5 has
> > a neighbor to r6 in AS 600. R3 and r6 both have a neighbor to r4 in AS
>400.
> > With this setup r1 picked the route through r2 as shown in the bgp table
> > showing 2 AS's through r2 (300 400) and 3 AS's through r5 (65000 600
>400) I
> > also checked it with a traceroute to verify that was happening. To make
>it
> > so that the AS path was the same I set an
> > AS-path prepend on r4 pointing to r3 so that r1 sees both r2 and r5 with
>3
> > AS's to pass through and should use the next determination in BGP's path
> > selection (origin then MED then closest IGP neighbor then BGP router
>ID).
> > The origin's are both incomplete since they are both redistributed into
>BGP
> > so the next path selection should be the MED. To test this I put a
> > route-map on r1 setting metrics to incoming routes from r2 and r5. I
>set it
> > up so that the subnet of 10.1.1.0 has a metric of 10 when coming from r2
>and
> > any other routes coming from r2 are set with a metric of 20. I did the
>same
> > thing on r5 with the subnet of 10.2.2.0 having a metric of 10 and all
>other
> > routes a metric of 20. With this setup all of the routes on r1 learned
> > through BGP go through r2 then are withdrawn and then all routes learned
> > through BGP go through r5. I took off the second statement off of both
> > route
> > maps setting the metric of all other routes to 20 and it works fine.
>Routes
> > to 10.1.1.1 go through r2 and routes to 10.2.2.2 go through r5 but right
> > when I add those route maps back specifying all other traffic to a
>metric of
> > 20 the same thing happens; all of the routes on r1 learned through BGP
>go
> > through r2 then are withdrawn and then all routes learned through BGP go
> > through r5.
> >
> > Thanks in advance,
> > Jeff CCIE bound in 17 days
> >
This archive was generated by hypermail 2.1.4 : Fri Jun 21 2002 - 06:45:12 GMT-3