Multiple IPs on a single hop and multiple IPs on ARP

[dyep110581]

Hi,

I just like to seek conclusion for the issue below.

DL01LEXB200-4DC#trace 157.227.86.77

Type escape sequence to abort.

Tracing the route to 157.227.86.77

1 10.10.1.2 0 msec

10.10.1.6 4 msec

10.10.1.2 0 msec

2 10.10.1.137 16 msec

10.10.1.133 8 msec

10.10.1.137 4 msec

3 10.10.1.162 0 msec 0 msec 4 msec

4 157.184.41.134 8 msec 12 msec 12 msec

5 157.184.43.130 68 msec 72 msec 68 msec

6 157.184.43.109 492 msec 552 msec 416 msec

7 157.227.86.77 452 msec 312 msec 308 msec

DL01LEXB200-4DC#

I just like to seek assistance on the above output of a trace route, why on the 1st hop and 2nd hop it has multiple IP adresses, what does that mean and why does it occur?

Also there's an instance that when i did #s ip arp command theres a part that it shows different IP address or multiple IP adresses mapped on a single MAC address, Like 5 IP Adresses on one Mac Address

Thanks

Dyep

[ohassairi]

may be this is because of NAT.

are you using NAT some where?

[Richard Burts]

Dyep

There are 2 parts to your question.

The first part is why the traceroute shows multiple addresses. The answer is that the router has multiple routes toward the destination and is doing per packet load sharing. Remember that traceroute sends 3 probe packets for each value of TTL. So the first packet is sent to one next hop, the second packet is sent to the other next hop and the third packet is sent to the original next hop. For example on the first hop you have these results:

Tracing the route to 157.227.86.77

1 10.10.1.2 0 msec

10.10.1.6 4 msec

10.10.1.2 0 msec

That means that the router has 2 paths toward 157.227.86.77. One path has a next hop of 10.10.1.2 and the other path has a next hop of 10.10.1.6. You should be able to confirm this by doing show ip route 157.227.86.77. The output should show 2 paths.

The other part of your question is why sometimes there is more than one IP address associated with a single MAC address in show ARP. Typically this is because those IP addresses are behind a router (and I have seen these results when behind a firewall as well). So the router (or firewall) is the next hop MAC address to get to those IP addresses.

HTH

Rick

[dyep110581]

I See, Thanks for that. Does the Firewall Do NAT/PAT thats why it shows multiple IPs on single MAC Add, or is it connected on multiple ports on the firewall? Just wondering how does the firewall do it. Thanks

[Richard Burts · Accepted solution]

Dyep

It is possible that the firewall is doing address translation for the addresses.

HTH

Rick

[dyep110581]

Thanks Rick

[Richard Burts]

Dyep

I am glad that our responses were helpful in resolving your question. Thank you for using the rating system to indicate that your question was resolved (and thanks for the rating). It makes the forum more useful when people can read a question and can know that there were responses which did help resolve the question.

The forum is an excellent place to learn about Cisco networking. I encourage you to continue your participation in the forum.

HTH

Rick