From: Vincent Mashburn (vmashburn@fedex.com)
Date: Tue Aug 29 2006 - 10:07:32 ART
Looks like you are using EIGRP with equal cost routes. Since traceroute
sends 3 packets at a time, I believe that what you are seeing is the
result of equal cost load-balancing.
Thanks
Vince Mashburn
Voice / Data Engineer
901-263-5072
CCVP, CCNP, CCDA,Network +
Cisco IP Telephony Support Specialist
Cisco IP Telephony Operations Specialist
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
nikhar.n@gmail.com
Sent: Tuesday, August 29, 2006 1:53 AM
To: ccielab@groupstudy.com
Subject: Weird Traceroute Behaviour...Need assistance
Hello All,
I'm currently preparing for the ccie lab exam as well as work as a
Network engineer for a local Enterprise. A few days ago i've come across
a traceroute behaviour that i can't fully decipher and need some
assistance with. Below is the topology diagram for the remote site with
a modified version of the ip addressing scheme.
The site comprises of 2 3825 wan routers which are connected to directly
over subnet .3 thru g0/1 interfaces as well over subnet .2. A point to
note is that g0/0 on both routers connect to switchports running in
access mode in vlan 2 on the 2 3750 series catalyst switches being used
as core switches as it's a small office. Both switches also have their
respective vlan 2 SVI's with the hosts ip's of 2.2 and 2.3. So
essentially, vlan 2 comprises of 4 routable interfaces (2 g0/0
interfaces on wan routers and 2 Routable SVI's on both the cores). Core
1 is the primary stp root and hsrp primary for the all user vlans. A
user switch is dual homed to both the cores. The user switch consists of
vlan 10 int with an ip 192.168.10.20. EIGRP is the IGP being used
throughout the corporate and is enabled on all l3 interfaces.
T1-Pri-circuit waiting for a backup circuit
|
| |
|g0/1 192.168.3.0/30 g0/1 |
Wan Router 1 ==================== WAN Router 2
g0/0 g0/0
192.168.2.5 192.168.2.6
| |
| HSrp: .1 (Core 1 Active) |
| |
| |
| |
Vlan int 2 - Core1 Vlan int 2 - Core2
192.168.2.2 192.168.2.3
192.168.2.20(Sec) 192.168.2.19 (sec)
| |
| L2 , All vlans |
Core 1 ============================= Core 2
| Vlan10 |
| 192.168.10.x/24 |
| |
| HSRP: .1 |
| |
| vlan 28 |
|___________User switch______________|
Issue:
When i traceroute to the vlan int 10 on user switch from either of the
wan routers. I get the following results.
trace 192.168.10.20
Type escape sequence to abort.
Tracing the route to 10.190.10.20
1 192.168.2.3 0 msec (core 2)
192.168.2.2 0 msec (core 1)
192.168.2.3 4 msec (core 2)
2 192.168.10.20 0 msec * 0 msec
Upon checking the route table, I can see the that there's two gateways
available for the packets
D 192.168.10.0/24 [90/3072] via 192.168.2.3, 7w0d,
GigabitEthernet0/0
[90/3072] via 192.168.2.2, 7w0d,
GigabitEthernet0/0
Upon checking the ip cef table, i can see that the packets will be sent
to 192.168.2.3 as per following
#sh ip cef exact-route 192.168.2.4 192.168.10.20
192.168.2.4 -> 192.168.10.20 : GigabitEthernet0/0 (next hop
192.168.2.3)
Question is, what does this trace route represent. I dont think it's a
routing loop since vlan 10 is a directly connected interface on both
cores and the packets should be switched locally. The part that really
puzzles me is the 2nd line of the trace route which seemingly suggests
packet bouncing between the cores before finally making its way back to
core 2(third line of trace route) and then getting delivered via the
directly connected interface of vlan 10.
Any feedback will be greatly appreciated on this.
TIA
This archive was generated by hypermail 2.1.4 : Fri Sep 01 2006 - 15:41:59 ART