07-24-2018 11:02 PM
Hi guys,
I've got a tricky one I'm trying to work out. I have 2x Cisco 2851's to provide redundancy to clients - I've configured VRRP for the LAN side as follows for both routers:
r1:
interface GigabitEthernet0/0.1
description Gi0/0.1 Office GW
encapsulation dot1Q 1 native
ip address 192.168.1.154 255.255.255.0
ip nat inside
ip virtual-reassembly
vrrp 1 description Office GW
vrrp 1 ip 192.168.1.254
vrrp 1 timers advertise msec 300
vrrp 1 preempt delay minimum 10
vrrp 1 priority 200
!
r2:
interface GigabitEthernet0/0.1
description Gi0/0.1 Office Gateway
encapsulation dot1Q 1 native
ip address 192.168.1.153 255.255.255.0
ip nat inside
ip virtual-reassembly
vrrp 1 description Office Gateway
vrrp 1 ip 192.168.1.254
vrrp 1 timers advertise msec 300
vrrp 1 preempt delay minimum 10
end
All client pc's have their gateway set as 192.168.1.254 which is working nicely. The problem I am trying to work out is with the WAN ip address. Let's say for example we have a public WAN ip of 123.123.123.123:
I've been reading up that you can cheat with VRRP and use a private IP with VRRP and then just put an ip route in for the public IP. The problem here is that NAT is trying to come from the primary ip instead of 123.123.123.123. I can ping 123.123.123.123 from any of the workstations but because it's trying to use NAT with 172.15.5.1, it's not a routeable subnet so I get no internet:
r1:
interface GigabitEthernet0/0.5
description Gi0/0.5 Office WAN
encapsulation dot1Q 5
ip address 172.17.5.254 255.255.255.0
ip flow ingress
ip nat outside
ip virtual-reassembly
vrrp 5 description Office WAN
vrrp 5 ip 172.17.5.1
vrrp 5 ip 123.123.123.123 secondary
vrrp 5 timers advertise msec 300
vrrp 5 preempt delay minimum 10
vrrp 5 priority 200
no cdp enable
!
ip route 123.123.123.120 255.255.255.248 GigabitEthernet0/0.5
access-list 1 permit 192.168.1.0 0.0.0.255
ip nat inside source list 1 interface GigabitEthernet0/0.5 overload
r2:
interface GigabitEthernet0/0.5
description Gi0/0.5 Office WAN
encapsulation dot1Q 5
ip address 172.17.5.253 255.255.255.0
ip flow ingress
ip nat outside
ip virtual-reassembly
vrrp 5 description Office WAN
vrrp 5 ip 172.17.5.1
vrrp 5 ip 123.123.123.123 secondary
vrrp 5 timers advertise msec 300
vrrp 5 preempt delay minimum 10
vrrp 5 priority 200
no cdp enable
!
ip route 123.123.123.120 255.255.255.248 GigabitEthernet0/0.5
access-list 1 permit 192.168.1.0 0.0.0.255
ip nat inside source list 1 interface GigabitEthernet0/0.5 overload
Basically I want to use VRRP with NAT so that both routers will always use the same WAN IP of 123.123.123.123. I did try changing the config to the following which worked but the problem here is that NAT wanted to use 123.123.123.121 as the NAT source instead of 123.123.123.123. Is there any way to get it to use 123.123.123.123 as the NAT source while still using VRRP or is this too complicated for what I'm after?
interface GigabitEthernet0/0.5
description Gi0/0.5 Office WAN
encapsulation dot1Q 5
ip address 123.123.123.121 255.255.255.248
ip flow ingress
ip nat outside
ip virtual-reassembly
vrrp 5 description Office WAN
vrrp 5 ip 123.123.123.123
vrrp 5 timers advertise msec 300
vrrp 5 preempt delay minimum 10
vrrp 5 priority 200
no cdp enable
Cheers, Mike
Solved! Go to Solution.
07-26-2018 10:09 AM
The problem is that the next hop router (which is the L3 on your private subnet used for transport) knows the path back to respond to packets (just because it will have a L3 interface in the same transport subnet which you use actually for NAT), however the next hop (of 123.123.123.123) has no idea of a route to your private subnet (172.17.5.x).
You would need either try to NAT to a public (routable) IP or to have your ISP do a second NAT of 172.17.5.x to a public IP (which I don't think it will happen).
Another solution is to use a public subnet for your transport (like a /29 or something to accommodate all your devices involved in routing).
Does this helps?
Calin
07-25-2018 12:49 AM
07-25-2018 09:40 AM
This resource will help you with the HA NAT, however this part "Basically I want to use VRRP with NAT so that both routers will always use the same WAN IP of 123.123.123.123" I see it as a problem.
Obviously I don't know how your WAN is connected but this will pose some challenges, first at L2 and the L3.
Do you have another switch on the the WAN side so you have L2 communication? The at L3 same ISP or different ISPs?
Seems to me that you want to have L3 HA on LAN and WAN plus SNAT.
Calin
07-25-2018 04:02 PM
Hi Calin,
both connections are through the same ISP with 2 different usernames. Radius is passing the subnet route through on both connections. There is a Cisco 3750 switch on the WAN side which takes the incoming connection from the NTD which I hand off via a vlan to both 2851's.
Cheers, Mike
07-26-2018 10:09 AM
The problem is that the next hop router (which is the L3 on your private subnet used for transport) knows the path back to respond to packets (just because it will have a L3 interface in the same transport subnet which you use actually for NAT), however the next hop (of 123.123.123.123) has no idea of a route to your private subnet (172.17.5.x).
You would need either try to NAT to a public (routable) IP or to have your ISP do a second NAT of 172.17.5.x to a public IP (which I don't think it will happen).
Another solution is to use a public subnet for your transport (like a /29 or something to accommodate all your devices involved in routing).
Does this helps?
Calin
07-26-2018 05:18 PM
Hi Calin,
No worries mate, yeah I thought this was the case. I ended up just using VRRP for the WAN ip for the exchange server's default gateway and left the single IP on each router that's part of the /29
Cheers, Mike
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