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rlh
New Member

Max number of secondary IP's on FE port?

Someone suggested elsewhere on this forum that the maximum number of secondary IP addresses which could be assigned to a 2621's Fast Ethernet port was six. I just applied twenty secondary addresses with no ill effects and everything seems to be working properly. So is there a limit? If so, what is it? Is there some other reason why large numbers of secondary addresses are a bad idea?

Thanks!

7 REPLIES
rlh
New Member

Re: Max number of secondary IP's on FE port?

Found this in P1C part 1, "IP Addressing and Services":

"You can specify an unlimited number of secondary addresses."

...so I'm not sure why someone on this forum would have said that there is a limit. Perhaps there is a PRACTICAL limit, one based on CPU load, etc. If so, I'd like to hear about it.

Thanks!

New Member

Re: Max number of secondary IP's on FE port?

r,

Secondary addresses are not advertized in EIGRP.

New Member

Re: Max number of secondary IP's on FE port?

I think secondary IP addresses are generally a bad idea.

The only case in which secondary are needed, is when you have multiple IP ranges on the same segment, which is just not good practice. Sometimes you don't have a choice, but if u get into a situation where you need unlimited IP addresses on an interface, it don't think your router is the problem.

Pim

rlh
New Member

Re: Max number of secondary IP's on FE port?

My situation is that this one FE port is driving an Aironet 350 wireless access point (AP). It serves several separate workgroups, each of which has a bridge-style wireless client. Each workgroup uses a separate subnet. So essentially I have a single Ethernet port going into the AP which must service multiple workgroups, each on a separate subnet.

I'd prefer to do this using subinterfaces (instead of secondary addresses) on the FE port, but I don' t think that will work with the AP. Might work with a switch that understands 802.1Q, but not in this scenario. I'd love to be proven wrong, though [grin].

New Member

Re: Max number of secondary IP's on FE port?

In your case.. you don't have a choice. :(

It's hard to separate wireless traffic while it is in the air.

pim

rlh
New Member

Re: Max number of secondary IP's on FE port?

But can you think of a way to do it using subinterfaces? It appears that I have to run 802.1Q, but if there's another way I'd prefer to use subint's instead of many secondary addresses.

Thanks!

New Member

Re: Max number of secondary IP's on FE port?

The only way I can see now, is using separate wireless base stations for separate networks. But that is very expensive and hard to maintain. You will have to configure each base station with different networks. And the wireless hosts as well..

Or you'll need access points that support VLANs.

I'm not sure these exist.

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