[quagga-users 7913] ibgp problems

[Sevinç]

Hi,
I have a few questions about using IBGP in Quagga.

1) Do we have to put the line "neighbor ..
ebgp-multihop" when we run BGP between two hosts in
the same AS, which are not directly connected?

2) I have a problem in disseminating the routes
learned from EBGP to the IBGP peers. That is, the
routes are obtained from an EBGP peering but not
advertised inside the AS. Is there a need to do a
special configuration for that?
**After a few tries, I found that the routes are
announced if a peer is at a different AS, but are not
announced if a peer is at the same AS.

Thank you,
Soner

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[Arnold Nipper]

Hi Soner,

Hi, I have a few questions about using IBGP in Quagga.
1) Do we have to put the line "neighbor .. ebgp-multihop" when we run
BGP between two hosts in the same AS, which are not directly
connected?

no. iBGP peers usually are not directly connected and multihop is more
or less the usual situation.

2) I have a problem in disseminating the routes learned from EBGP to
the IBGP peers. That is, the routes are obtained from an EBGP peering
but not advertised inside the AS. Is there a need to do a special
configuration for that? **After a few tries, I found that the routes
are announced if a peer is at a different AS, but are not announced
if a peer is at the same AS.

Would you mind to share the config with us. First guess is that the bgp
subcommand "no synchronization" is missing

If BGP synchronization is enabled, there must be a match for the prefix
in the IP routing table in order for an internal BGP (iBGP) path to be
considered a valid path. BGP synchronization is enabled by default [may
be it's time to set "no synchronization" as default as it is from IOS
12.2(8)T and later]




Arnold, AN45

[Sevinç]

Hi,

Post by Sevinç

Post by Sevinç
2) I have a problem in disseminating the routes

learned from EBGP to

Post by Sevinç
the IBGP peers. That is, the routes are obtained

from an EBGP peering

Post by Sevinç
but not advertised inside the AS. Is there a need

to do a special

Post by Sevinç
configuration for that? **After a few tries, I

found that the routes

Post by Sevinç
are announced if a peer is at a different AS, but

are not announced

Post by Sevinç
if a peer is at the same AS.

Would you mind to share the config with us. First
guess is that the bgp
subcommand "no synchronization" is missing
If BGP synchronization is enabled, there must be a
match for the prefix
in the IP routing table in order for an internal BGP
(iBGP) path to be
considered a valid path. BGP synchronization is
enabled by default [may
be it's time to set "no synchronization" as default
as it is from IOS
12.2(8)T and later]

I think "no synchronization" is about the routes that
originate from the local AS, and advertised to other
ASes, right? If yes, my case is different in which the
problem is to advertise externally originated routes
inside the local AS.

Inside the local AS, I run a IBGP full mesh, and one
of the router talks to a different ISP router (EBGP).
Although the routes are delivered to that router, they
are not disseminated in the full mesh. Any thoughts

Thank you.
Soner

Post by Sevinç
Arnold, AN45
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[J.T. Moore]

Soner,


1. IBGP (hosts in the same AS) does not require
the multihop option. IBGP is multihop by default.

2. Do the IBGP peers have a route(s) to the next hop(s)
learned by the EBGP peer? If they don't, the
IBGP peers will discard the routes from EBGP as invalid.
Based on your description, it sounds like the IBGP
peers don't have routes the next hop.

The next hop is not automatically changed when
advertised to IBGP peers, but it is changed when
advertised to EBGP or confederation peers.

If your IBGP peers don't have a route the next hop
learned by BGP, you will need to do one of the following:

1. Add static routes to the next hop(s) learned from EBGP
on all the IBGP peers

2. Run an internal routing protocol such as OSPF to between
the IBGP peers that advertises the next hop(s) learned from
EBGP

3. Use route maps to change the next hop when advertising
the routes learned from EBGP to the IBGP peers

4. Use a confederation for you IBGP routers. Another benefit
of confederations, is that they don't require full mesh.

Also, if there are multihops between the IBGP peers,
the IBGP peers will need routes to each other through the
intermediate nodes. Routes through intermediate nodes in a
multihop configurations are required for IBGP, EBGP, and
confederations. These routes can either be static or carried
in an internal routing protocol so as OSPF.

Regards,

J.T.



-----Original Message-----
From: Soner "Sevinç [mailto:***@yahoo.com]
Sent: Saturday, January 06, 2007 2:29 PM
To: quagga-***@lists.quagga.net
Subject: [quagga-users 7913] ibgp problems

Hi,
I have a few questions about using IBGP in Quagga.

1) Do we have to put the line "neighbor ..
ebgp-multihop" when we run BGP between two hosts in
the same AS, which are not directly connected?

2) I have a problem in disseminating the routes
learned from EBGP to the IBGP peers. That is, the
routes are obtained from an EBGP peering but not
advertised inside the AS. Is there a need to do a
special configuration for that?
**After a few tries, I found that the routes are
announced if a peer is at a different AS, but are not
announced if a peer is at the same AS.

Thank you,
Soner

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