From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Sat Apr 12 2008 - 09:32:03 ART
Hi Nit,
Traceroute sends three packets with an identical TTL, and continues
increasing the TTL and sending three packets until a port (or host)
unreachable is received back. Your traceroutes show only one hop (left
hand column). The packets are not bouncing between interfaces, rather
each of the packets which comprise the traceroute are being sent out
different interfaces in turn.
This means the traceroute packets alternate between having one of two
different source addresses. When ICMP replies are being sent back,
different interfaces are selected to get to those two source addresses,
and so ICMP replies sent to R5 have different source addresses as well.
The last two traces may be showing the effect of ICMP rate limiting on
the other router. This is common and helps reduce the impact to the CPU
of some DoS attacks. If a ttl exceeded is received, but no port
unreachable, then it will appear as if there is another hop. If port
unreachable packets are received within the timeout period you will see
that hop timeout.
I believe CEF switching supports load balancing of up to 16 paths.
Paul.
Joseph Brunner wrote:
> CEF which supersedes the routing table will cause the oldest route to be
> used.
>
> Disable cef
>
> No ip cef
>
> And then tell us what you found.
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
> Nitro Drops
> Sent: Friday, April 11, 2008 9:53 PM
> To: ccielab@groupstudy.com
> Subject: EIGRP - Unequal-Cost LoadBalancing
>
> Guys,
>
> was practising this scenario.
>
> R4 S2/1 (155.1.45.4/24) >> 64K Serial 64K>> (155.1.45.5/24)S2/1 R5
> R4 S2/0 (155.1.0.4/24) >> 256 K Frame Relay 256K >> (155.1.0.5/24) S2/0 R5
> R4 Loopback 0 - 150.1.4.4
> R5 Loopback 0 - 150.1.5.5
>
> Variance calculated is 4.
>
> R5:
> router eigrp 100
> variance 4
>
>
>
>
>
>
>
>
>
>
>
>
>
> R5#sh ip eigrp neighbors
> IP-EIGRP neighbors for process 100
> H Address Interface Hold Uptime SRTT
> RTO Q Seq
> (sec) (ms) Cnt Num
> 1 155.1.0.4 Se2/0 150 00:42:28 189 1134 0 29
> 0 155.1.45.4 Se2/1 12 00:44:48 191 2280 0 30
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> R5#sh ip
> route
> Gateway of last resort is not set
> 155.1.0.0/24 is
> subnetted, 2 subnets
> C 155.1.0.0 is
> directly connected, Serial2/0
> C 155.1.45.0 is
> directly connected, Serial2/1
> 150.1.0.0/24 is
> subnetted, 2 subnets
> C 150.1.5.0 is
> directly connected, Loopback0
> D 150.1.4.0 [90/40640000] via 155.1.45.4,
> 00:00:46, Serial2/1
> [90/10639872] via 155.1.0.4,
> 00:00:46, Serial2/0
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> R5#trace 150.1.4.4
> Type escape sequence to abort.
> Tracing the route to 150.1.4.4
> 1 155.1.45.4 156
> msec
> 155.1.0.4 148 msec
> 155.1.45.4 28 msec
>
>
>
>
>
>
>
>
>
>
>
>
>
>
>
> R5#trace 150.1.4.4
> Type escape sequence to abort.
> Tracing the route to 150.1.4.4
> 1 155.1.0.4 176 msec
> 155.1.45.4 128
> msec
> 155.1.0.4 152 msec
>
>
>
>
>
>
>
>
>
>
>
> R5#trace 150.1.4.4
> Type escape sequence to abort.
> Tracing the route to 150.1.4.4
> 1 155.1.0.4 168 msec
> 180 msec *
>
>
>
>
>
>
>
>
>
>
>
> R5#trace 150.1.4.4
> Type escape sequence to abort.
> Tracing the route to 150.1.4.4
> 1 155.1.0.4 152 msec
> 40 msec *
>
>
> I can see the packets being load-balanced when tracing from R4 to R5's
> loopback. Did 4 traces continuously and noticed the follows
>
> Q1.) For the 1st 2 traces, how come the packets reaches R4's S2/1 interface,
> it will go to R4's S2/0 interface again before hitting R4's loopback? The
> same goes for the 2nd trace, it will go to R4's S2/0 interface 1st, followed
> by R4's S2/1 interface before reaching R4's loopback.
>
> Q2) For the 3rd and 4th traces, it hits the R4's loopback0 immediately as
> next hop, without hitting R4's S2/0 or S2/1.
>
>
> Appreciate any kind advice.
>
>
> Cheers
> Nit
>
>
>
>
>
>
>
>
> _________________________________________________________________
> Easily manage multiple email accounts with Windows Live Mail!
> http://www.get.live.com/wl/all
>
>
> Pass the CCIE in six weeks, Guaranteed!
> http://www.certscience.com/CCIE
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
>
>
> Pass the CCIE in six weeks, Guaranteed!
> http://www.certscience.com/CCIE
> _______________________________________________________________________
> Subscription information may be found at:
> http://www.groupstudy.com/list/CCIELab.html
Pass the CCIE in six weeks, Guaranteed!
http://www.certscience.com/CCIE
This archive was generated by hypermail 2.1.4 : Thu May 01 2008 - 08:25:50 ART