From: Bill Hill (bhill@xxxxxxxxxx)
Date: Mon Mar 11 2002 - 00:17:35 GMT-3
Hmmm, I don't know about that.
If I am at a router, and have established a peer with an EBGP neighbor, unless
I run a routing protocol, I am going to have to create a static route to that d
estination. In the same manner, the ISP will create a static to get back to my
loopback via that same link. In the event of a failure of a link in a multi-h
omed organization, I'm not sure that I would be advertising via that other rout
er or via that other path as a route to my original peer.
When doing EBGP via an ISP, they usually prefer to use the directly connected I
P address of the physical link.... unless you are using multiple connections to
the same ISP and do loopback peering. Along the same lines, and correct me if
I am wrong, they are not going to advertise or use an additional path/route to
your loopback or physical interface address.
I guess in some situations, and if the stars were in alignment, it may be possi
ble, but I would want to change what you said of "high possibility" to remote p
ossibility.
Is this correct? Did that make any sense? (It's late and I have had a few gla
sses of wine. ;-) ) I don't work for an ISP but have seen many multi-homed netw
orks.
-Bill
-----Original Message-----
From: Jason Sinclair [mailto:sinclairj@powertel.com.au]
Sent: Sunday, March 10, 2002 11:01 PM
To: Bill Hill; RSiddappa@NECBNS.com; tsabry@houston.sns.slb.com;
ccielab@groupstudy.com
Subject: RE: Update-source in EBGP
Bill,
Generally you are correct regarding the TTL, however consider when you are
multihomed and physically lose connectivity to your peer. If the TTL is too
high, there is a real possibility that your BGP tcp connection will
re-establish the long way round through your other peer. This makes life
interesting!!
Cheers,
Jason Sinclair
Manager, Network Support Group
POWERTEL
Ground Level, 55 Clarence Street,
SYDNEY NSW 2000
AUSTRALIA
office: + 61 2 8264 3820
mobile: + 61 416 105 858
* sinclairj@powertel.com.au
-----Original Message-----
From: Bill Hill [mailto:bhill@sgdata.com]
Sent: Monday, 11 March 2002 12:29
To: RSiddappa@NECBNS.com; tsabry@houston.sns.slb.com;
ccielab@groupstudy.com
Subject: RE: Update-source in EBGP
the "ttl" is optional, if you do not specify, it will
default to 255 and will just increase the possible diameter of your network,
ugly maybe but shouldn't hurt anything. (I am sure there are some security
guys out there freaking out right about now!)
-----Original Message-----
From: RSiddappa@NECBNS.com [mailto:RSiddappa@NECBNS.com]
Sent: Sunday, March 10, 2002 9:23 PM
To: Bill Hill; tsabry@houston.sns.slb.com;
ccielab@groupstudy.com
Subject: RE: Update-source in EBGP
What will happen If I do nto specify the hops ?
I have seen it taking 255. What effect will it have ?
R.
-----Original Message-----
From: Bill Hill [mailto:bhill@sgdata.com]
Sent: Sunday, March 10, 2002 8:02 PM
To: Tarek Sabry; ccielab@groupstudy.com
Subject: RE: Update-source in EBGP
You can have any IP from one router peer to any other IP of
another router
as long as there is a route between the two.
You only require ebgp-multihop if the 2 peer routers IP
addresses are not
directly connected using the same linke, ie: 2 physical
endpoints. If so,
you count the number of layer-3 hops between the 2 endpoints
and use that as
the parameter. And just to state the obvious, ebgp-mutihop
is ony used when
you connect different AS's.... ie EBGP, not IBGP.
HTH
-Bill
-----Original Message-----
From: Tarek Sabry [mailto:tsabry@houston.sns.slb.com]
Sent: Sunday, March 10, 2002 8:37 PM
To: ccielab@groupstudy.com
Subject: Update-source in EBGP
Quick question:
Do I have to have symmetrical configs on both sides? Can I
have one loopback
on one AS try to peer with th serial on the other AS?
Also do I have to have "ebgp-multihop" whenever I use
"update-source lo0"?
Thanks
Tarek
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