From: Peter van Oene (pvo@xxxxxxxxxxxx)
Date: Mon Aug 05 2002 - 10:55:02 GMT-3
Darryl
At 10:58 PM 8/5/2002 +1200, Darryl Munro wrote:
>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.
Nothing you've quoted above really contradicts what Jason has said. Jeff
basically steps you through the normal settings a BGP next-hop is most
likely to have in a traditional AS. As I mention in my other post (which
is very similar to Jason's since I didn't see he already answered the
question :) this feature is most likely aimed at MPLS based networks where
one is working to provide hooks into the MPLS forwarding plane from the BGP
control plan to enable various MPLS provided topologies.
>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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