From: Paul Cosgrove (paul.cosgrove@heanet.ie)
Date: Sat Apr 12 2008 - 09:55:08 ART
Or rather..
If NO port unreachable packets are received within the timeout period
you will see that hop timeout.
Paul Cosgrove wrote:
> 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
>>
>>
>>
>>
>>
>>
>>
>>
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>
>
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