-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Thanks for the through reply and the verifying that I have a decent grip on policy routing. I'm less concerned that i'm not following the author's train of thought than I am the the concept in general.
I agree that I muddied the waters by bringing bgp into the picture. I understand the usage of route-maps in bgp relates to controling bgp routing information between neighbors not in the actual routing of data packets as it does with policy routing. I appreciate the example, though, it helped me further clarify things. Thanks again, John Chuck's Long Road wrote: | you pretty much understand how it works. You might be muddying the waters a | bit by bringing BGP into the picture | comment below: | | | | ""John Matney"" wrote in message | [EMAIL PROTECTED]">news:[EMAIL PROTECTED]... | |>-----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) | | | | CL: sure. makes sense. I'm not sure why the authors would take this tack, as | policy routing applies only to inbound traffic. at best, it can set next | hop, as you note. But nothing that the policy sets is untouchable by other | routers, same autonomous ystem or not. | | | |>~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. | | | | CL: yep | | | |>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? | | | | CL: yep | | |>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. | | | | CL: you can send a packet anyplace. that doesn't mean the destination router | has to accept it. | | CL: but mixing policy routing and BGP in your mind is probably not a good | idea. the BGP settings that are done via route-maps associated with neighbor | statements apply to BGP routing information. Policy routing applies to data | packets, not to routing protocol information. Does that make sense? | | CL: examples: | | router bgp 9902 | neighbor 1.1.1.1 remote-as 9990 | neighbor 1.1.1.1 route-map take_my_sttings out | neighbor 1.1.1.1 route-map screw_your_settings in | | as opposed to | | interface s 0 | ip policy route-map zzyzx | | | |>Make sense? I'm a bit confused as to what the authors are getting to in |>this passage. Could someone help? | | | | CL: HTH | | |>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----- | | | | | - -- 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 iD8DBQE9Yrq3SRPIWojudpURAlOYAKCN0aK4OmWODW1vqCXXvjpHfucnogCfS8z2 UyXADenqyRqCNTwZ3tOiIiQ= =5d1G -----END PGP SIGNATURE----- Message Posted at: http://www.groupstudy.com/form/read.php?f=7&i=51794&t=51689 -------------------------------------------------- FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
