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3550 obtaining default route and dns addresses

mschooley
Level 1
Level 1

ok, I may be missing something simple, but I have 2 3550's no ip routes, no default gateway set, no dns servers set, yet I can ping outside addresses, traceroute to them and resolve names miraculously, any ideas where these default routes might be coming from

!

interface Vlan30

ip address 10.20.30.21 255.255.255.0

!

interface Vlan39

ip address 10.20.39.12 255.255.255.0

!

ip classless

ip http server

!

!

control-plane

!

!

line con 0

line vty 0 4

password 7 070A20581D0C1C09

login

line vty 5 15

password 7 02050D480809

no login

!

end

ussw01#sho ip route

Default gateway is not set

Host Gateway Last Use Total Uses Interface

ICMP redirect cache is empty

ussw01#

28 Replies 28

Mike,

Do you think reloading C3550 will solve this issue? (grin)

Don't forget to post the output I asked for If you're available to do that.

Thanks,

Toshi

no as it is happening on two switches. odds of same glitch is small

Hey, now that I got the 2 of you guys here, check this out for a sec:

I have a switch access port configured for switchport voice vlan 580.

Then I have the SVI for 580.

Then I plug the laptop into the switchport and try to PING SVI. Doesnt work.

When I remove the voice vlan command and make it a regular data vlan (switchport access vlan 580), it works.

Im wondering why. Have you encountered this before?

Taking a guess, I would think that the voice vlan command lets the switchport expect a voice packet with voice signalling information in the header. When it doesnt see that, it just kills the packet.

IS that what you think is happening?

Thanks

Victor

i think that your laptop isn't sending cdp so switchport doesnt' recognize a cisco phone on the end so doesnt use voice vlan.

Victor,

My turn, I think that switch is waiting for tagged packets and then untag it before sending it out to SVI(voice). Your pc can tag packets. NO! Voice Vlan? That's why IP-Phone has to do some with the packets to separate data(untagged) vlan and voice vlan.

Toshi

the way that the switch determines to use the voice vlan is that it recognizes a cisco ip phone via cdp, no phone, no voice vlan. yes your pc can tag packets, but unless the switch sees an ip phone plugged in via cdp it wont use the voice vlan and the port will stay and access port.

MIKE,

Please correct me if I'm wrong. I used to do the following commands with Avaya IP phone. Well, Don't get me wrong. I indeed love cisco ip phone.

!

Interface f0/1

switchport mode access

switchport access vlan 100

switchport voice vlan 300

!

Well,Avaya will not know about cdp. What it does is that it will tag voice packets and leave data traffic as untag and send them to the switch.

Toshi

what do you get when you show cdp neighbors

Mike,

I got nothing from cdp but interface is up and works like a charm. I think that CDP is pretty cool for cisco ip phone. IP-Phone will learn about you already configured. That's cool. Avaya engineer(not me(grin)) has to manually configure voice vlan on the avaya phone itself to tell it. Part of data traffic will depend on what we configured at the port because they are coming with untagged packets.

Toshi

I was under the impression that the cisco switch wouldn't use the voice vlan unless it saw a phone via cdp, but the avaya gets its voice vlan via manual config or dhcp, so maybe as long as the device attached supports q tagging it will work. That would also mean that his laptop would have to have a nic that supported 802.1q tagging otherwise would be put in data vlan. I am verifying about the switchport

Mike,

You're right.

Off topic, My country many customers use Avaya and Nortel. What about yours? and how are you doing? (grin)

Thanks

Toshi

yes a lot use avaya and nortel and my issue is resolved. proxy arp was enabling the routing and the ip domain lookup to the 255.255.255.255 was resolving the names.

Mike,

That's great. But I'm a bit confused. I'm not sure that why the switches do ARP for 4.2.2.1. Am I missing something?

Thanks

Toshi

"proxy arp was enabling the routing"

Ehem...seems like someone suggested that at the beginning of this thread. Gee, I wonder who it was. ;-)

I'll take my 5 POINTS now...from BOTH of you...

Thank you...thank you (blowing kisses to an endearing crowd)

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