From: Jonathan V Hays (jhays@jtan.com)
Date: Mon Sep 29 2003 - 16:11:40 GMT-3
I think your first post was correct.
Also, your examples are bit confusing since you don't say what router
the configs are from and where 1.1.1.2 and 2.2.2.2 are located.
A better example would show rtr1 in one AS and rtr2 in another AS and
state which router the displayed configs are from.
From "Internet Routing Architectures, Second Edition" page 211:
"...whenever we talk about taking steps to affect inbound traffic we are
really talking about applying attributes to outbound routing
announcements because how our routes are learned by others affects how
traffic is routed inbound. Similarly, whenever we talk abou taking steps
to affect outbound traffic, we are talking about applying attributes to
inbound routing announcements because how our network learns routes
affects how outbound traffic is routed."
--- With respect to your own routers and your own AS:1. You set metrics OUTBOUND to neighbors in another AS to allow the other AS to decide which inbound entry to your AS to use for a given prefix (if the other AS doesn't decide to ignore your metrics).
2. You set local preference on INBOUND traffic FROM your neighbors. This local preference attribute is automatically distributed to other routers in your AS and is used for your AS routers to decided which outbound exit (from your AS) to take to get to a given prefix external to your AS.
HTH,
Jonathan
-----Original Message----- From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of Ken.Farrington@barclayscapital.com Sent: Monday, September 29, 2003 1:48 PM To: ccielab@groupstudy.com Subject: RE: BGP BOLD Statements
actually, I can use both attributes to set the inbound path selection correct?
ie in the following two BGP examples.
Ethernet +-------------------------+ | | rtr1 AS 65001 rtr2 | | +-------------------------+ Serial
-------------SET-MED--------------------------------- ! router bgp 65001 neighbor 1.1.1.2 remote-as 65001 neighbor 1.1.1.2 route-map SET-MED-ETHERNET out neighbor 2.2.2.2 remote-as 65001 neighbor 2.2.2.2 route-map SET-MED-ETHERNET out ! route-map SET-MED-SERIAL permit 10 match as-path 11 set metric 1000 ! route-map SET-MED-SERIAL permit 20 ! ! no route-map SET-MED-ETHERNET route-map SET-MED-ETHERNET permit 10 match as-path 11 set metric 2000 ! route-map SET-MED-ETHERNET permit 20
or
-------------SET-LOCALPREF---------------------------------
router bgp 65001 neighbor 1.1.1.2 remote-as 65001 neighbor 1.1.1.2 route-map SET-LOCALPREF-ETHERNET out neighbor 2.2.2.2 remote-as 65001 neighbor 2.2.2.2 route-map SET-LOCALPREF-ETHERNET out ! route-map SET-LOCALPREF-SERIAL permit 10 match as-path 11 set local-pref 80 ! route-map SET-MED-SERIAL permit 20 ! ! route-map SET-LOCALPREF-ETHERNET permit 10 match as-path 11 set local-pref 90 ! route-map SET-MED-ETHERNET permit 20 !
-----Original Message----- From: Ken.Farrington@barclayscapital.com [mailto:Ken.Farrington@barclayscapital.com] Sent: 29 September 2003 18:24 To: ccielab@groupstudy.com Subject: BGP BOLD Statements
Hello, Can I just think of the two BGP attributes LOCAL_PREF and MULTI-EXIT_DISC in the following way.
LOCAL_PREF = To influence a path to a network outside my AS from my AS -> outbound path selection (shared between iBGP peers) MULTI-EXIT-DISC = To influence to an external AS which path to take coming to a network in my AS <- inbound path selection (used "ONLY" with eBGP peers)
Is this about the crucks of it, or it it dangerous to think of these two attribs this way. Just during my study, my brain is full up and I cant get too much more in there me thinks.
Many thx indeed.
Ken
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