BGP is an application layer protocol since it uses TCP for
communicating with neighbors.
Other protocols like OSPF and EIGRP use their own IP protocol number
and are not relying on TCP or UDP.
Why BGP is not changing the next-hop while advertising in iBGP is
definitely a design decision. Which is an answer to your Why :-)
The reason behind is that you are letting the underlying IGP choose
which path to take to the BGP next-hop. Then it depends on your IGP
set-up how the traffic gets through the network. Of course there are a
lot of ways to overcome this, but you really need to ask yourself if
you want to that. If you don't want to or are not allowed to advertise
the link connecting to the eBGP neighbor to be advertised in your
network, then you have no other option that to issue a next-hop-self
for example.
Read RFC 1771 (http://www.ietf.org/rfc/rfc1771.txt) for more exact
explanations.
--
Regards,
Rick Mur
CCIE2 #21946 (R&S / Service Provider)
Juniper JNCIA-ER & JNCIA-EX
MCSA:Messaging, MCSE
Sr. Support Engineer – IPexpert, Inc.
URL: http://www.IPexpert.com
On 18 aug 2009, at 16:14, Taqdir Singh wrote:
Hi Prakash
I know we can use next hop self . but that is not answer to my
question..
my question....is why BGP is so made to carry next hop of ebgp in
internal AS ?
AS100(C)----e-bgp---AS200(A)----ibgp----AS200(B)
Why BGP was not made so that router A automatically advertise routes
to B with next hop of itself.. as in case of all the other routing
protocols ?
and Why BGP is application layer ?
Sincerely,
Taqdir Singh
91-9911709496
Do today what others won't So you can live tomorrow what others can't
From: prakash patel <[email protected]>
To: [email protected]; [email protected]
Sent: Tuesday, 18 August, 2009 7:31:20 PM
Subject: RE: [OSL | CCIE_RS] RIP and BGP are application layer
protocol
RIP is the oldest one where some hosts can learn RIP routes from
router. ON host, RIP has to run as application ..am I right?
BGP can change by doing "next-hop-self" so you have that option.
Date: Tue, 18 Aug 2009 19:20:16 +0530
From: [email protected]
To: [email protected]
Subject: [OSL | CCIE_RS] RIP and BGP are application layer protocol
Can any1 please clear , how RIP and BGP are application layer
protocols ?
Why BGP is so made to carry the E-BGP next-hop in internal AS ?
Sincerely,
Taqdir Singh
91-9911709496
Do today what others won't So you can live tomorrow what others can't
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