Setting up 2620xm with cable modem SB4100 problem

[CiscoPractitioner]

Hi everyone,

I'm trying to set up a home network with Cisco 2620xm (1fa) with cable modem SB4100 through a 2950 switch, but can't get it to work.

I set up 2 Vlans.. Vlan 10 fa port 2 for cable modem, Vlan 20 as access ports for the rest. Port 1 is set as trunk which connects to router.

Router has two sub interfaces fa0/0.10 172.16.1.0 as IP NAT outside network for Vlan 10 and fa0/0.20 192.168.1.0 as IP NAT INSIDE network for Vlan 20.

IP route 0.0.0.0 0.0.0.0 172.16.1.1
ACL was set as standard to permitting the networks and Nat is linked with ACL and set to overload.

There is a catch in which my ISP uses DHCP assigned ip, however, it hasn't changed for a very long time.

There are definite faults in my setup but I don't know exactly what it is or if it's even workable because I read on other forums that a 'NAT on a stick' is needed with a loopback address.

Also there is the problem with the cable modem with one max mac, so I switched CDP, Keepalives, STP off on port 2.

Can someone please point me to the right direction?

 

[burtsbees]

The router will still send out ARP packets. Do you have the modem set up in bridge mode? If not, then it's the modem that NATs not the router. If it is in bridge mode, and you still do PPPoE/A on the modem, then you need to NAT to a loopback and make it the public ip address of the vlan 10 address, either static or from dhcp...

int fa0/0
no ip add
no shut
!
int fa0/0.10
description from_ISP_DHCP_public_ip
encaps dot1q 10
ip add dhcp
!
int fa0/0.20
description LAN
encaps dot1q 20
ip add 192.168.1.1 255.255.255.0
ip nat inside
!
int loopback0
ip add unnumbered fa0/0.10
ip nat outside
!
ip route 0.0.0.0 0.0.0.0 lo0

Or, bridge and do pppoe/oa on the router. You'd have to find out if it is pppoe or oa, and the encaps on the modem-facing SVI.

/


tim@tim-laptop ~ $ sudo apt-get install windows
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package windows...Thank Goodness!

 

[CiscoPractitioner]

Hi Burtsbees,

Thx for your reply, tried your set up but still not working.

I am unable to find out if my cable modem is in bridge mode or not, 192.168.100.1 doesn't give me much info.

On loopback0 what is unnumbered fa0/0.10? I tired a couple of addresses in place of it but with no luck.

And 'bridge and do pppoe/oa on the router. You'd have to find out if it is pppoe or oa, and the encaps on the modem-facing SVI.'

How would I go about finding out this information?

 

[ISPKing]

First there is no type of ppp needed at all, this is a cable modem, not dsl. And the sb4100 is a pure modem, no ip manipulation. You need to make sure that the dhcp request is getting to the Cable modem, the ip unnumbered is referencing your svi for its address, in which nat will be performed on. Do a port mirror (span) and confirm you see dhcp requests on the Port connected to the Cable modem.

What your doing is kind of a run around, although i think burts is right on, I am not sure of a better way to do it, but it is a pita. If possible sell your 2620xm and get a 2621xm. That would really simplify the process.


CCNP

 

[CiscoPractitioner]

Hey ISPKing,

Thanks for ur reply,

This is what I got form SPAN on the port, it doesn't say anything about DHCP requests.

Type : Local Session
Source Ports :
Both : Fa0/2
Destination Ports : Fa0/1
Encapsulation : Native
Ingress: Disabled

I didn't know that ip unnumbered was a command but now I do thanks to u guys, but when I input the line it says 'Point-to-point (non-multi-access) interfaces only'

 

[ISPKing]

You need to hook up wireshark to the mirrored port and watch the packets.

CCNP