From: Darryl Munro (Darryl.Munro@xxxxxxxxxxxxxxxxxx)
Date: Mon Aug 05 2002 - 07:58:46 GMT-3
Hi Jason,
You have just blown away my understanding of the next hop attribute:
As per Page 102 of Doyle Volume II
And this is a direct plaj:
The NEXT_HOP Attribute
As the name implies, this well-known mandatory attribute describes the
IP address of the next-hop router on the path to the advertised
destination. Blah Blah (one finger typing exhausts me)
If the advertising router and receiving router are in different
autonomous systems (external peers), the NEXT_HOP is the IP address of
the advertising router's interface.
If the advertising router and the receiving router are in the same AS
(inetrnal peers), and the NLRI of the update refers to a destination
within the same AS, the NEXT_HOP is the address of the neighbour that
advertised the route.
If the advertising router and the recieving router are internal peers
and the NLRI of the update refers to a destination in a different AS,
the NEXT_HOP is the address of the external peer from the route was
learned.
Have I totally misunderstood all of the above in light of your comment
as follows:
To sum it up the rules of BGP state that if a route is learned via iBGP
then next hop info does not change and we can use the bgp next-hop self
statement to modify this. With eBGP peers, the next hop info is modified
at each eBGP router (in each AS) so that the next hop appears as the
advertising router.
Or am I just misinterpreting what you are saying. Maybe I am just a dumb
&*&*& Kiwi and our country can't play rugby.
Cheers
-----Original Message-----
From: Jason Sinclair
To: 'Dennis Laganiere'; ccielab@groupstudy.com; cisco@groupstudy.com
Sent: 5/08/02 14:26
Subject: RE: What the heck is BGP Next Hop Propagation?
Dennis,
This link explains it:
http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/120newft
/120
limit/120st/120st16/st_bgpnh.htm
This feature allows you to modify the next-hop attribute when
configuring
route-reflectors and also allows you to send next-hop info to eBGP peers
that is not modified as per the normal rules of next hop changes when
sending an advertisement to an eBGP neighbour. To sum it up the rules of
BGP
state that if a route is learned via iBGP then next hop info does not
change
and we can use the bgp next-hop self statement to modify this. With eBGP
peers, the next hop info is modified at each eBGP router (in each AS) so
that the next hop appears as the advertising router. To modify this you
can
use the info in the attached link.
Please let me know if this clarifies this, or if you would like further
explanation.
Regards,
Jason Sinclair CCIE #9100
Manager, Network Control Centre
POWERTEL
55 Clarence Street,
SYDNEY NSW 2000
AUSTRALIA
office: + 61 2 8264 3820
mobile: + 61 416 105 858
email: sinclairj@powertel.com.au
-----Original Message-----
From: Dennis Laganiere [mailto:Dennis@laganiere.net]
Sent: Tuesday, 6 August 2002 09:27
To: ccielab@groupstudy.com; cisco@groupstudy.com
Subject: What the heck is BGP Next Hop Propagation?
In a semi-random CCO search I came across "BGP Next Hop Propagation",
but
reading over the few links I've found isn't enough for me to figure it
out.
I've looked through several BGP books and found nothing. I also tried an
archive search without results. Anybody seen this before? (I've got to
find
a new hobby... :-)
--- Dennis
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