From: Chuah Eng Wee (chuahew@xxxxxxxxxxxxxxx)
Date: Mon Jul 26 1999 - 07:20:27 GMT-3
Hi Jason,
Yes, u should use loopbacks to avoid flaps in EBGP. However, u have
to take note that the loopback is not directly connected. So u
need to use ebgp-multihop.
RTA
-----
int s0
ip addr Y.Y.Y.Y
router bgp 1
neighbor X.X.X.X remote-as 2 where X.X.X.X is RTB loopback
neighbor X.X.X.X ebgp-multihop
RTB
-----
int lo0
ip address X.X.X.X
router bgp 2
neighbor Y.Y.Y.Y remote-as 1 where Y.Y.Y.Y is RTB directly connected s0
neighbor Y.Y.Y.Y upadate-source lo0
HTH
Eng Wee
>Bill I think I found the problem. My neighbor is a loopback interface(I
>thought you should use loopbacks to avoid flaps?!?).
>
>Once I moved the neighbor statement from using the loopback to the Serial0,
>BGP found the remote and is working fine.
>
>I thought you should use point neighbors to loopbacks on remote routers for
>stability? Is this not true ? I could ping it, I could telnet to it, I tried
>with/without sync, etc.
>
>Looking at Caslow p.466 he mentions I should have looked at the
>update-source option in the neigbor command. I bet this is the problem.
>Maybe I'll repro this tomorrow as I'm tired tonight - jason
>
>
>----Original Message Follows----
>From: Bill Carter <bcarter@family-net.net>
>To: Jason Aarons <jaarons@hotmail.com>
>Subject: Re: BGP config
>Date: Thu, 22 Jul 1999 22:48:49 -0500
>MIME-Version: 1.0
>>From bcarter@family-net.net Thu Jul 22 20:49:04 1999
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>1999 22:53:50 -0500 (CDT)
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>References: <19990723024855.29996.qmail@hotmail.com>
>
>The route has to be in the IGP. BGP will not advertise a network until all
>of
>the routers in an IBGP know about the route. If static routes are in both
>routers tables then the route will be advertised in BGP. Remember the main
>difference between BGP and Interior protocols. IGP's network statements
>describe
>the nets that will participate in routing. BGP advertises what networks can
>be
>reached. It's like the Chicken and the Egg problem. The BGP routers within
>an
>AS have to all know how to reach a network BEFORE they will advertise the
>network.
>
>Here is an example from Cisco CCIE Fundamentals: Network Design and Case
>Studies:
>AS 100 Router E
>AS 100 Router A====(Network 2.0.0.0)===Router B AS 100
>
>AS 300 Router C (network 170.10.0.0) Router D AS 400 (network
>175.10.0.0)
>
>Routers A, B and E are in AS 100 2.0.0.0. (IBGP neighbors)
>Router C is AS 300 170.10.0.0
>Router D is AS 400 175.10.0.0
>Router A and Router C are EBGP neighbors
>Router B and Router D are EBGP neighbors
>" If Router B advertises to AS 400 (RD) that it can reach 170.10.0.0 before
>Router E learns about the network via IBGP, traffic coming from Router D to
>Router B with a destination of 170.10.0.0 will flow to Router E and be
>dropped."
>
>This is because Router E advertises network 170.10.0.0, but when traffic
>comes
>into Router E it doesn't know to forward the traffic to Router A. Therefore
>Router E, A and B have to agree on how to forward traffic destined for a
>network
>before the traffic reaches any of the routers and needs to be forwarded to
>that
>network. Synchronization forces the routers to plan ahead.
>
>Think of it this way. If you saw an advertisement for 1999 BMW's for $200
>dollars, you wouldn't jump in your car and drive until you knew what car
>dealer
>to go to.
>
>
>
>Jason Aarons wrote:
>
> > If I didn't want to do the "no sync", is there other option to add static
> > routes ? To me it seems crazy that the Internal routing protocol must
>know
> > about the external network before the External routing protocol will talk
>to
> > the External routing protocol neighbor.
> >
> > I was reading more about this...but haven't yet fully grasped it.
> >
> > ----Original Message Follows----
> > From: Bill Carter <bcarter@family-net.net>
> > To: Jason Aarons <jaarons@hotmail.com>
> > Subject: Re: BGP config
> > Date: Thu, 22 Jul 1999 20:48:19 -0500
> >
> > You need to add no sync to BGP 300. The 16.0.0.0 route is not in the
>route
> > tables for the 2 routers. They will not accept routes not known by
>internal
> > routing protocols. Try debug ip bgp events and debug ip bgp updates.
> >
> > Jason Aarons wrote:
> >
> > > Do anyone have some BGP "show ip bgp neighbor" or "show ip bgp
>summary"
> > > outputs between two ASs that are talking ?
> > >
> > > I have two routers connected but am not sure what the "show ip bgp
> > summary"
> > > should show ? I can ping both ways, etc....
> > >
> > > !
> > > interface Loopback0
> > > ip address 16.0.0.1 255.0.0.0
> > > !
> > > interface Serial1
> > > ip address 172.16.1.2 255.255.255.252
> > > clockrate 148000
> > > !
> > > router bgp 300
> > > network 16.0.0.0
> > > neighbor 10.0.0.1 remote-as 100
> > > !
> > > ip classless
> > > ip route 10.0.0.0 255.0.0.0 Serial1
> > > !
> > > END
> > > iowa#ping 10.0.0.1
> > >
> > > Type escape sequence to abort.
> > > Sending 5, 100-byte ICMP Echos to 10.0.0.1, timeout is 2 seconds:
> > > !!!!!
> > > Success rate is 100 percent (5/5), round-trip min/avg/max = 12/14/16
>ms
> > > iowa#
> > >
> > > iowa#show ip bgp neigh
> > > BGP neighbor is 10.0.0.1, remote AS 100, external link
> > > Index 1, Offset 0, Mask 0x2
> > > BGP version 4, remote router ID 0.0.0.0
> > > BGP state = Idle, table version = 0
> > > Last read 00:00:15, hold time is 180, keepalive interval is 60
>seconds
> > > Minimum time between advertisement runs is 30 seconds
> > > Received 0 messages, 0 notifications, 0 in queue
> > > Sent 0 messages, 0 notifications, 0 in queue
> > > Connections established 0; dropped 0
> > > Last reset 00:00:16, due to : User reset request
> > > No. of prefix received 0
> > > External BGP neighbor not directly connected.
> > > No active TCP connection
> > > iowa#show ip bgp summary
> > > BGP table version is 2, main routing table version 2
> > > 1 network entries (1/3 paths) using 208 bytes of memory
> > > 1 BGP path attribute entries using 96 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
> > >
> > > Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down
> > > State/PfxRcd
> > >
> > > 10.0.0.1 4 100 0 0 0 0 0 never
>Idle
> > > iowa#
> > >
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