Hi, Could you give me the relevant configs explaining why when I traceroute to 12.83.43.9 on route-server.ip.att.net, the first hop is " j6300.cbbtier3.att.net (12.0.1.202)". However, when I type "show ip route 12.83.43.9", the RIB shows, "* 12.122.83.91, from 12.122.83.91, 7w0d ago". I asked someone who is knowledgeable about the matter, and he seems to think that you can change the interface which sends back ICMP unreachables, but I don't know how to do this on my own simulated equipment. Also, I have noticed that when I traceroute to any ip address on the internet from my home connection, the last hop that's in common with all traceroutes is 12.83.43.9. This is a hop after several hops which seem to be filtered. What is the purpose of this IP? Are there any publically available documentation that would help me understand the process of aggregating multiple DSLAMs, etc on my at&t u-verse connection? I am a CCNA/CCNP student in college and this would help me understand WANs better. Thanks Michael R. Sabino michael.rocco.sabino@gmail.com
Did you do a show ip route for 12.122.83.91? It's probably a loopback of the nearest BGP peer it may not be the actual next hop interface IP though. Not sure about the blocked hops, but I can think of a few explanations. Overall the point of that router is to provide a view of the route table and not the physical hops from one point to another. Since actual customer traffic wouldn't flow through the route server the first few hops are probably irrelevant. 2011/11/4 Michael Sabino <michael.rocco.sabino@gmail.com>
Hi,
Could you give me the relevant configs explaining why when I traceroute to 12.83.43.9 on route-server.ip.att.net, the first hop is " j6300.cbbtier3.att.net (12.0.1.202)". However, when I type "show ip route 12.83.43.9", the RIB shows, "* 12.122.83.91, from 12.122.83.91, 7w0d ago".
I asked someone who is knowledgeable about the matter, and he seems to think that you can change the interface which sends back ICMP unreachables, but I don't know how to do this on my own simulated equipment.
Also, I have noticed that when I traceroute to any ip address on the internet from my home connection, the last hop that's in common with all traceroutes is 12.83.43.9. This is a hop after several hops which seem to be filtered. What is the purpose of this IP?
Are there any publically available documentation that would help me understand the process of aggregating multiple DSLAMs, etc on my at&t u-verse connection?
I am a CCNA/CCNP student in college and this would help me understand WANs better.
Thanks
Michael R. Sabino michael.rocco.sabino@gmail.com
On Fri, Nov 04, 2011 at 03:39:43PM -0500, Michael Sabino wrote:
Could you give me the relevant configs explaining why when I traceroute to 12.83.43.9 on route-server.ip.att.net, the first hop is " j6300.cbbtier3.att.net (12.0.1.202)". However, when I type "show ip route 12.83.43.9", the RIB shows, "* 12.122.83.91, from 12.122.83.91, 7w0d ago".
A couple things here: 12.122.83.91 is the BGP next-hop in the RIB. It needs to be resolved. In this case it's being resolved via a /13 static route: route-server>sho ip route 12.122.83.91 Routing entry for 12.120.0.0/13 Known via "static", distance 1, metric 0 Redistributing via bgp 65000 Advertised by bgp 65000 Routing Descriptor Blocks: * 12.0.1.1, via GigabitEthernet0/1 Route metric is 0, traffic share count is 1 In real life it'd probably be resolved via an IGP such as OSPF or IS-IS, but this is a route server, not a transit router. So, the real next-hop is 12.0.1.1. You can also verify this with the following, since it's a Cisco box: route-server>show ip cef 12.83.43.9 12.0.0.0/9 nexthop 12.0.1.1 GigabitEthernet0/1 However, you don't see 12.0.1.1 in the traceroute because it looks to be the VRRP address of the Juniper J6300 upstream router (just judging by the hostname): route-server>sho arp 12.0.1.1 Protocol Address Age (min) Hardware Addr Type Interface Internet 12.0.1.1 81 0000.5e00.0101 ARPA GigabitEthernet0/1 The MAC address is a giveaway that it's VRRP, since 00-00-5E-00-01 is reserved by IANA for VRRP (IPv4 only): http://tools.ietf.org/html/rfc5798#section-7.3 The Juniper router will send back ICMP TTL-exceeded messages from the real IP on its interface, which appears to be 12.0.1.202. Hope this helps. - Mark -- Mark Kamichoff prox@prolixium.com http://www.prolixium.com/
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Michael Sabino