Weird Tracert..

gouki2005gouki2005 Posts: 197Member
ok look this topology

[IMG]file:///C:/Users/Gerson/AppData/Local/Temp/moz-screenshot.png[/IMG]topolog.jpg?t=1285546176
Router3 and 4 are running Static,Rip,Ospf
Router 0 just static
Router 2 just rip
Router 1 just ospf

this the weird thing if i do a tracert from PC0 to PC1 this the path..

1 5 ms 6 ms 6 ms 192.168.1.1
2 6 ms 7 ms 4 ms 192.168.3.2
3 9 ms 8 ms 13 ms 192.168.8.2
4 19 ms 13 ms 12 ms 192.168.2.2

so according to this this..the path..look

topoloffffg.jpg?t=1285546503


Hows that posible jump from router 0 to router 1 the next logic hop is 192.168.6.2 and this the router 0 Routes

S 192.168.1.0/24 [1/0] via 192.168.3.1
S 192.168.2.0/24 [1/0] via 192.168.6.2
C 192.168.3.0/24 is directly connected, Serial0/0/0
C 192.168.6.0/24 is directly connected, Serial0/0/1

you see the router doesnt know the 192.168.8.0 network

explain me..plz

Comments

  • mikej412mikej412 Posts: 10,090Member
    Look at how trace route works. It send an ICMP packet with a ttl of 1 and waits for a reply. Then is sends another with a ttl of 2 and waits for a reply... etc.

    Depending on your routing configurations and routing tables there may be multiple network paths and the ICMP packets may be "load balanced" -- so you may get the first response to the ttl=1 packets from one path, the ttl=2 response from a router further along the 2nd path, etc....

    Edit: hopefully I just didn't blow a homework assignment/lab where you were supposed to figure this out for yourself icon_eek.gif
    :mike: Cisco Certifications -- Collect the Entire Set!
  • wastedtimewastedtime Posts: 586Member
    First off you need to remember 2 things. First Traceroute sends out consecutive packets with incrementing TTL (Time To Live). Second OSPF will load balance equal cost links (by default if I remember right). This is more then likely this is the routes the packets took.

    wastedtime-albums-forum-picture151-route.png
    With the order of them being black, red, green, and blue.
  • gouki2005gouki2005 Posts: 197Member
    wastedtime wrote: »
    First off you need to remember 2 things. First Traceroute sends out consecutive packets with incrementing TTL (Time To Live). Second OSPF will load balance equal cost links (by default if I remember right). This is more then likely this is the routes the packets took.

    wastedtime-albums-forum-picture151-route.png
    With the order of them being black, red, green, and blue.

    still dont understand why the tracert doesnt show the 192.168.5.2 hop..if some packets pass there
  • wastedtimewastedtime Posts: 586Member
    If you did enough traceroutes you should see all of the routes. The reason it looks like that is due to the nature of OSPF load balancing and how Traceroute commands works.

    Traceroute works on the idea that a router is suppose to send a a TTL exceeded message back to the sender when the TTL reaches 0. The TTL get decremented at every router. Traceroute will send packets with incrementing Time To Live values in the IP header (ex. 1 then 2 then 3.....ect). When it gets a TTL exceeded packet back it records the round trip time and the ip of the router that sent the message back.

    Due to the fact that you have OSPF running, it will load balance the packets it gets across those 3 routes (provided they have equal cost). So when the router reports back saying the TTL has exceeded it may have taken a different path then the first traceroute packet.
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