Re: BGP question.
- To: "'Jumpot Phuritatkul'" <howdy at nectec dot or dot th>
- Subject: Re: BGP question.
- From: Barry Raveendran Greene <bgreene at cisco dot com>
- Date: Sat, 21 Jun 1997 18:33:22 +0800
- Cc: "'apops at apnic dot net'" <apops at apnic dot net>
- Encoding: 200 TEXT
- Sender: email@example.com
Hello Jumpot, Here's the policy routing option. I need a little time to check a config with my colleagues. Here's a example config for Router B (RTB). I'm guessing on your config, so I picking thing out of the air. Instead of IP addresses, I'm using '[Router A]' to describe the link. delete the '[Router A]' and fill in with the real IP addresses. ! interface serial 0/0 description LINK TO ROUTER A (Upstream) ip address [Router A] ip policy route-map Upstream_Policy ! interface serial 0/1 description LINK TO ROUTER C (Down Stream Customer) ip address [Router C] ! interface serial 0/2 description LINK TO ROUTER D (National IXP) ip address [Router D] ! interface ethernet 1/0 description LINK TO LOCAL LAN ! access-list 1 permit any [C's CIDR block] ! route-map Upstream_Policy permit 10 match ip address 1 set ip next-hop [Router C] ! ! This policy routing example will take all the packets from A that match an address in C's CIDR block and forward them out C's interface. All other traffic will use the forward table. Hence, you can set the BGP local preference for C's CIDR block to use D. So this give you: 1) A to go to C via path (1) A-B-C (Achieved with policy routing) 2) B to go to C via path (2) B-D-C (Achieved with BGP local pref) Barry Jumpot Phuritatkul wrote: >Thanks for your advice. > >I have a 7507 for B and 7513/VIP for C. at B, I have many networks that >connected with many slots and I want them to use path 2)B-D-C except >2 serial interface to two of my upstreams use path 1)A-B-C . > >Can you give me another solution by use BGP setting command? > >Jumpot- > >On Thu, 19 Jun 1997, Barry Raveendran Greene wrote: > >> Hello Jumpot, >> >> This one is a little difficult. Your objective is the following: >> >> 1) A to go to C via path (1) A-B-C >> 2) B to go to C via path (2) B-D-C >> >> Here's the problem. You have one forward table (i.e. sh ip route on a Cisco >> router). This will hold the route selected from the routing protocols. You >> can manipulate the route selection process (i.e. like using the local >> preference in BGP), but you will still only get the "best" entry in the >> forward table selected for use. When you have two "equal" cost entries in >> the forward table, Cisco "round robins" packets evenly over the two equal >> entries (this does not mean load balance since packets are not of equal >> size). >> >> So all packets coming into a router will use the forward table to determine >> which interface to "forward" the packets. >> >> Now for the possible "hack" that may work (not guaranteed) if you have a >> 7500 w/VIP cards. With Cisco's VIP architecture and distributed switching, >> forward tables are pushed out to the VIP processors. If you place the >> serial connection for "A" and "C" on the same VIP card. Put "B" on another >> VIP card with the LAN interfaces from B's site on that same VIP card the >> serial link from "D" (preferable on a different bus). Packets coming in >> from A will prefer the interface on the same VIP card - C. Packet from B's >> LAN interfaces will prefer the D interface. >> >> I'm not sure that will work as described. Plus, this only takes care of >> traffic flows coming from A (downstream). For Internet traffic in Asia, >> that's 60%-80% for the traffic. >> >> If you have a 7500 w/VIP card and you wish to pursue this hack, let me >> know. >> >> Barry >> >> >> Jumpot Phuritatkul wrote: >> >> >But from my intention, B will announce C and D networks by originating >> >from B because I don't want A to see AS C and D. So that A will see C >> >and D networks by only AS-path B . >> >>From your solution, at B will get C's routes with 2 AS-path (C and D-C) >> >and B will choose D-C to be the best path because of setting localprefs. >> >Consequently, B will announce the best path of C to A with originating >> from B >> >then A will see C'routes from B which was only one AS-path B and it is the >> >best path that B send to A that is path (2) but I want A to go to B via >> >path (1). How can I do ? >> > >> > (1) >> > [A] --------[B]----------------[C] >> > | (2) | >> > +------[D]---------+ >> > >> >-Jumpot >> > >> > >> >On Wed, 18 Jun 1997, Scott Huddle wrote: >> > >> >> If B localprefs D higher it will prefer that route to C >> >> (and yet still have it if D goes down) B can announce >> >> C and D to A and it (A) will select BC over >> >> BDC by virtue of path length. >> >> >> >> Did I miss something? >> >> >> >> -scott >> >> >> >> At 06:00 PM 6/18/97 +0700, Jumpot Phuritatkul wrote: >> >> >Hi, >> >> > Would someone give me a solution for this problem? >> >> > >> >> > (1) >> >> > [A] --------[B]----------------[C] >> >> > | (2) | >> >> > +------[D]---------+ >> >> > >> >> > There are 4 networks of A, B, C and D. >> >> > A,B,C and D have their own Autonomous System Numbers. >> >> >A is upstream provider of B. B want to announce B,C and D's networks >> with >> >> >AS origin of B to A . I want A to go to C via path (1) A-B-C , and B to >> go >> >> >to C via path (2) B-D-C . How can I set BGP command at B,C and D? >> >> >Please help me solve this problem. >> >> > >> >> >Regards, >> >> >Jumpot Phuritatkul >> >> >Network Technology Lab. >> >> >NECTEC, Thailand . >> >> > >> >> > >> >> >> >_________________________________________________________________________ >> >> >To unsubscribe: send "unsubscribe" to apops-request at apnic dot net >> >> >> >------------------------------------------------------------------------ >> >> > >> >> > >> >> >> > >> -- >> -- >> -- >> Barry Raveendran Greene | || || | >> Senior Consultant | || || | >> Corporate Consulting Engineering | |||| |||| | >> tel: +65 738-5535 ext 235 | ..:||||||:..:||||||:.. | >> e-mail: bgreene at cisco dot com | c i s c o S y s t e m s | >> >> > -- -- -- Barry Raveendran Greene | || || | Senior Consultant | || || | Corporate Consulting Engineering | |||| |||| | tel: +65 738-5535 ext 235 | ..:||||||:..:||||||:.. | e-mail: bgreene at cisco dot com | c i s c o S y s t e m s | _________________________________________________________________________ To unsubscribe: send "unsubscribe" to apops-request at apnic dot net ------------------------------------------------------------------------