Using multiple public IPs on 800 series

[nbaker011]

Hello, I have several public IPs from my ISP and am trying to figure out what is the easiest way of taking advantage of the dual WANs on the 891F for this. I see a lot of posts around different ISPs and failover, but this would be two connections to the same modem using both Gi8 and Fa0 to get two different public IP addresses for the 891F. I'm ok routing separate VLANs per WAN (preferable actually). I'm trying to figure out what is the easiest configuration to accomplish this. Any pointers appreciated.

Thanks,

Nick.

[Reza Sharifi]

Hi,

If both connections go to the same modem and you have 2 next hops (one for gi8 and one for fa0), you could simply configure 2 default routes one pointing to the IP on the other side of gi8 and one pointing to the IP on the other side of fa0 interface.  This way if one like goes down you have a second link to use and also you can load balance traffic on both links.

HTH

[nbaker011]

Thanks, trying to go through the configuration for this.

I seem to be stuck getting both the Fa0 an Gi8 interfaces to simultaneously maintain the DHCP lease from the modem.

I have the modem assigning the two different public IP addresses based on the MAC of the respective Fa0/Gi8 interfaces.

When either one is enabled the address gets configured, but if both are enabled only one of the interfaces maintains its DHCP lease. Looking at "show dhcp lease", one of the interfaces cycles though Selecting, Requesting, Purging. I see the correct IP address assigned briefly, but then the state goes to Purging.

This behavior happens on the interface that is enabled last, so if both interfaces are shutdown and I enable Fa0 first then Gi8, Fa0 will be stable but Gi8 will not, and vice versa.

Anything obvious I should look at?

Config:

!

interface FastEthernet0
 ip address dhcp
 ip access-group incoming_acl2 in
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip nat outside
 ip inspect autosec_inspect out
 ip virtual-reassembly in
 ip verify unicast source reachable-via rx allow-default 100
 duplex auto
 speed auto
 no cdp enable

!

!
interface GigabitEthernet8
 ip address dhcp
 ip access-group incoming_acl in
 no ip redirects
 no ip unreachables
 no ip proxy-arp
 ip nat outside
 ip inspect autosec_inspect out
 ip virtual-reassembly in
 ip verify unicast source reachable-via rx allow-default 100
 duplex auto
 speed auto
 no cdp enable
!

Cisco891F#show dhcp lease
Temp IP addr: 70.234.xx.aa  for peer on Interface: FastEthernet0
Temp  sub net mask: 255.255.255.248
   DHCP Lease server: 192.168.1.254, state: 5 Bound
   DHCP transaction id: 26EC
   Lease: 86400 secs,  Renewal: 43200 secs,  Rebind: 75600 secs
Temp default-gateway addr: 70.234.xx.cc
   Next timer fires after: 11:54:45
   Retry count: 0   Client-ID: cisco-0042.68f5.0d9a-Fa0
   Hostname: Cisco891F
Temp IP addr: 70.234.xx.bb  for peer on Interface: GigabitEthernet8
Temp  sub net mask: 255.255.255.248
   DHCP Lease server: 192.168.1.254, state: 11 Purging
   DHCP transaction id: 2189
   Lease: 86400 secs,  Renewal: 0 secs,  Rebind: 0 secs
   Next timer fires after: 00:00:18
   Retry count: 0   Client-ID: cisco-0042.68f5.0da2-Gi8
   Hostname: Cisco891F

[nbaker011]

I tried assigning the IP addresses manually on 891F the which seems to provide some insight into what is going on. Because i'm connected to the same modem, the addresses have to be in the same subnet. so:

Gi8: 70.234.xx.249 255.255.255.248

Fa0: 70.234.xx.250 255.255.255.248

The router complains:

% 70.234.xx.248 overlaps with GigabitEthernet8

So I guess the WANs have to be different subnets?