You are right in that you are missing the point. The statement is correct - you can decide that voice traffic to the next AS should take path A, and all other traffic take path B (and you do this with multiple route-maps within each router), but once you deliver the datagram to the next AS, it is up to them as to how they route that traffic, ie, you are not doing something like strict source routing in which you specify exactly each hop the packet should take. There is no mechanism for you to tell the next AS that this traffic should take an expedited path within their environment, unless they have similar routing policies as you do.
That's the way I read it. Now I'm not sure about the BGP med attributes (I'm getting the books next week!) but I simply read the statement at face value. Richard Larkin Technical Specialist Communications Services InfoHEALTH Alliance (a DoH/DMR Consulting Alliance) * Phone: (+61) 8 9318 6257 * Fax: (+61) 8 9318 6390 * Mobile: (+61) 41 731 0578 * mailto:[EMAIL PROTECTED] -----Original Message----- From: John Matney [mailto:[EMAIL PROTECTED]] Sent: Tuesday, 20 August 2002 9:46 AM To: [EMAIL PROTECTED] Subject: Policy Routing Question [7:51689] -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 I've been reading the Cisco CCNP Cert Guide in partial preparation for the BSCI exan and I've come across a bit in the Policy Routing section that I just don't understand. The text states: "Policy routing does not allow traffic sent into another autonomous system to take a different path from the one that would have been chosen by that autonomous system." (pp. 551) ~From the reading, I understand that policy routing is configured on an inbound interface and can filter on either source or both source and destination addresses. PR, via a route map, can set properties such as precedence, QoS and next-hop. All of these items only really have relevance on the router in which policy routing is being done. In other words, once the router policy routes the packet and specifies, for instance, the next-hop interface. Now, if that next-hop router chooses to drop, fragment or otherwise mangle the packet so be it, the first router has no control over it anymore, its done its job. So then, how does this quote apply? Perhaps, I'm completely missing the point (wouldn't be the first time). A router can only do what its configured to do. If I tell a packet to take path a to get to network b but network b would perfer its incoming traffic to come in via path c, the most network a can do to prevent this is to drop incoming traffic via path a. Correct? Even if we were running a EGP such as BGP4 and the distant router had a MED set to perfer path c, I could still push packets via path a given that I knew it existed. Make sense? I'm a bit confused as to what the authors are getting to in this passage. Could someone help? Thanks, John - -- http://pgp.mit.edu:11371/pks/lookup?op=get&search=0x88EE7695 Key fingerprint = DBD7 6AE2 E7BE 1572 B245 BF54 4913 C85A 88EE 7695 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.1.90-nr1 (Windows XP) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQE9YZ1hSRPIWojudpURAoAQAKCMOZu+TQcZOSW39mqtZooDzRGoBwCgm+Ti YMQGvYkbcXWMn/IhQZTmpnk= =hAME -----END PGP SIGNATURE----- Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51698&t=51689 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
