bgp question

ardealulardealul Member Posts: 1 ■□□□□□□□□□
hi guys, this is my first post with my first question:

Basically, can someone explain to me the bellow `sh ip bgp sum`s ?

The setup is quite simple: 2x 2811 routers that connect to 2x ISPs and that have themselves (the routers) set as iBGP Peers. Filters are only set on the out to isp (so that i don't become a transit AS), not between the iBGP peers. HSRP enabled on both internal int of the routers (BGP shouldn't care though about it)

Question1: x.x.x.76 gets 268025 prefixes (subnets) from neighbor r.r.r.r & x.x.x.96 gets 268323 prefixes (subnets) from s.s.s.s. Why does x.x.x.96 say that he gets only 119006 prefixes (routes) from x.x.x.76 and not the 268025 that x.x.x.76 from r.r.r.r ? Same for the other Router (x.x.x.96).

Question 2: shouldn't the maximum of bgp activity paths equal (example for x.x.x.96) to 268323+119006+1(=287330) and not the 4391402 that it reports ?

Question 3: A prefix is a subnet in the `sh ip bgp` table right ?

Question 4: A path is every row in the `sh ip bgp` table for a distinct prefix/subnet, right ?

Question 5: What are (also example for x.x.x.96) 316682/46726 & 4778733/4391402 ?

Question 6(most important): If these two routers are connected to 2 ISPs via 2 different bandwidth connections (let's say x.x.x.96 has more bandwith to the metropolitan network), how can i tweak bgp so that all traffic (incoming&outgoing) from/to metro IPs comes/goes via him and notx.x.x.76 ?

On x.x.x.76 i get:

BGP activity 280508/10567 prefixes, 887554/386303 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
x.x.x.96 4 <AS> 102061 89429 1454987 0 0 17:00:10 233225
r.r.r.r 4 <AS> 102290 57 1454938 0 0 00:28:27 268025

on x.x.x.96 i get:

BGP activity 316682/46726 prefixes, 4778733/4391402 paths, scan interval 60 secs

Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
y.y.y.y 4 <AS> 1683 69378 7085866 0 0 20:14:22 1
x.x.x.76 4 <AS> 802772 726567 7085920 0 0 16:58:53 119006
s.s.s.s 4 <AS> 238859 69264 7085866 0 0 20:14:20 268323

Comments

  • TurgonTurgon Banned Posts: 6,313
    ardealul wrote:
    hi guys, this is my first post with my first question:

    Basically, can someone explain to me the bellow `sh ip bgp sum`s ?

    The setup is quite simple: 2x 2811 routers that connect to 2x ISPs and that have themselves (the routers) set as iBGP Peers. Filters are only set on the out to isp (so that i don't become a transit AS), not between the iBGP peers. HSRP enabled on both internal int of the routers (BGP shouldn't care though about it)

    Question1: x.x.x.76 gets 268025 prefixes (subnets) from neighbor r.r.r.r & x.x.x.96 gets 268323 prefixes (subnets) from s.s.s.s. Why does x.x.x.96 say that he gets only 119006 prefixes (routes) from x.x.x.76 and not the 268025 that x.x.x.76 from r.r.r.r ? Same for the other Router (x.x.x.96).

    Question 2: shouldn't the maximum of bgp activity paths equal (example for x.x.x.96) to 268323+119006+1(=287330) and not the 4391402 that it reports ?

    Question 3: A prefix is a subnet in the `sh ip bgp` table right ?

    Question 4: A path is every row in the `sh ip bgp` table for a distinct prefix/subnet, right ?

    Question 5: What are (also example for x.x.x.96) 316682/46726 & 4778733/4391402 ?

    Question 6(most important): If these two routers are connected to 2 ISPs via 2 different bandwidth connections (let's say x.x.x.96 has more bandwith to the metropolitan network), how can i tweak bgp so that all traffic (incoming&outgoing) from/to metro IPs comes/goes via him and notx.x.x.76 ?

    On x.x.x.76 i get:

    BGP activity 280508/10567 prefixes, 887554/386303 paths, scan interval 60 secs

    Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
    x.x.x.96 4 <AS> 102061 89429 1454987 0 0 17:00:10 233225
    r.r.r.r 4 <AS> 102290 57 1454938 0 0 00:28:27 268025

    on x.x.x.96 i get:

    BGP activity 316682/46726 prefixes, 4778733/4391402 paths, scan interval 60 secs

    Neighbor V AS MsgRcvd MsgSent TblVer InQ OutQ Up/Down State/PfxRcd
    y.y.y.y 4 <AS> 1683 69378 7085866 0 0 20:14:22 1
    x.x.x.76 4 <AS> 802772 726567 7085920 0 0 16:58:53 119006
    s.s.s.s 4 <AS> 238859 69264 7085866 0 0 20:14:20 268323


    You are multihoming and the questions you are asking are very basic things. I suggest you talk to your ISPs and don't change anything on that router until you speak to them.

    Here's a link to some essential reading.

    http://www.nanog.org/mtg-0510/pdf/smith.pdf
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