From: nikhar.n@gmail.com
Date: Tue Aug 29 2006 - 03:53:18 ART
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