From: Brian Dennis (bdennis@internetworkexpert.com)
Date: Tue Sep 05 2006 - 14:44:30 ART
If you think about how each packet is switched on the routers
(originating router, first hop router, etc), it should help you
understand what you are seeing.
Brian Dennis, CCIE #2210 (R&S/ISP-Dial/Security)
bdennis@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
Toll Free: 877-224-8987
Direct: 775-745-6404 (Outside the US and Canada)
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
nikhar Wilder
Sent: Tuesday, September 05, 2006 9:26 AM
To: Vincent Mashburn
Cc: ccielab@groupstudy.com
Subject: Re: Weird Traceroute Behaviour...Need assistance
Thanks Vincent. I think that's the case. Something mind boggling is,
that Trace always sends 3 packets with varying TTL's regardless of the
hop/node it's ran from but yet i only see this kinda output from the
router closest to the destination but not from anywhere else. Maybe
there's more to it or there's something i'm missing.
On 8/29/06, Vincent Mashburn <vmashburn@fedex.com> wrote:
>
> 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
>
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