What's a VRF?
- A VRF is a Virtual Routing and Forwarding instance, it's basically a virtualization technique for IOS routers. Each VRF has its own interfaces (you cannot put a L3 interface in 2 different VRFs), it has its own routing table and everything.
- You create a VRF by typing:
ip vrf my-out-vrf
- You assign interfaces to a VRF using:
int fa0/0
ip vrf forwarding my-out-vrf
- You create a static route and you look at the routing table for a VRF using:
ip route vrf my-out-vrf 10.1.1.0 255.255.255.0 192.168.5.5
sho ip route vrf my-out-vrf
- lots of commands and features are "vrf-aware", just use the question mark to find out...
ping vrf my-vrf-out 10.1.1.2
sho ip cef vrf my-vrf-out 10.1.1.2
ip nat inside source list 199 interface fa0/0 vrf my-vrf-out overload
...
- VPNs are MAGIC because they can have their encrypted traffic in 1 VRF and the decrypted traffic in another VRF.
The typical use case for this is an ISP that provides VPN service to multiple enterprise customers on the same box, the users and branches connect using internet for the encrypted traffic, but the decrypted traffic needs to go to the private network of each separate customer and this traffic cannot be mixed.
Terminology
- ivrf : Inside VRF, the VRF that contains the clear-text traffic (before encryption for outbound flows and after decryption for inbound flows)
- fvrf : Front-door VRF (or outside VRF), the VRF that contain the encrypted traffic
- global VRF: the routing instance that is used if no specific VRF is defined. If no VRF-aware config is used, everything is done in the global VRF and all interfaces are in the global VRF.
Configuration
Crypto map-based with ivrf=cust1-vrf and fvrf=internet-vrf
ip cef
ip vrf cust1-vrf
!
ip vrf internet-vrf
!
!
crypto keyring internet-keyring vrf internet-vrf
pre-shared-key address 10.1.1.2 key cisco123
!
crypto isakmp policy 10
encr 3des
authentication pre-share
group 2
crypto isakmp profile cust1-ike-prof
vrf cust1-vrf
keyring internet-keyring
match identity address 10.1.1.2 255.255.255.255 internet-vrf
isakmp authorization list default
!
crypto ipsec transform-set esp-3des-sha esp-3des esp-sha-hmac
!
crypto map mymap 10 ipsec-isakmp
set peer 10.1.1.2
set transform-set esp-3des-sha
set isakmp-profile cust1-ike-prof
match address 199
reverse-route
interface GigabitEthernet0/0
description internet WAN link
ip vrf forwarding internet-vrf
ip address 10.1.1.3 255.255.255.224
crypto map mymap
!
interface GigabitEthernet0/1
description cust1 private VRF
ip vrf forwarding cust1-vrf
ip address 192.168.88.20 255.255.255.0
!
interface loopback10
ip vrf forwarding cust1-vrf
ip address 1.1.1.1 255.255.255.255
ip route vrf internet-vrf 0.0.0.0 0.0.0.0 10.1.1.1
access-list 199 permit ip host 1.1.1.1 host 2.2.2.2
To remember:
- "vrf <ivrf>" on isakmp profile
- fvrf on match statement of isakmp profile
- keyring tagged with fvrf
- RRI for route leaking (otherwise we don't hit the crypto map) or a static route like "ip route vrf cust1-vrf 2.2.2.2 255.255.255.255 GigabitEthernet0/0 10.1.1.1" (note that the route is on the ivrf routing table but points to an interface of the fvrf)
- interfaces in their respective VRF
- proper routes in each VRF
Tunnel-protection with ivrf=cust1-vrf and fvrf=internet-vrf
ip cef
ip vrf cust1-vrf
!
ip vrf internet-vrf
!
crypto keyring internet-keyring vrf internet-vrf
pre-shared-key address 10.1.1.2 key cisco123
!
crypto isakmp policy 10
encr 3des
authentication pre-share
group 2
!
crypto isakmp profile cust1-ike-prof
keyring internet-keyring
match identity address 10.1.1.2 255.255.255.255 internet-vrf
isakmp authorization list default
local-address GigabitEthernet0/0
!
crypto ipsec transform-set esp-3des-sha esp-3des esp-sha-hmac
!
crypto ipsec profile cust1-ipsec-prof
set transform-set esp-3des-sha
set isakmp-profile cust1-ike-prof
!
!
interface Tunnel200
ip vrf forwarding cust1-vrf
ip address 172.16.4.4 255.255.255.0
tunnel source GigabitEthernet0/0
tunnel destination 10.1.1.2
tunnel mode ipsec ipv4
tunnel vrf internet-vrf
tunnel protection ipsec profile cust1-ipsec-prof
!
interface GigabitEthernet0/0
description internet WAN link
ip vrf forwarding internet-vrf
ip address 10.1.1.3 255.255.255.224
!
interface GigabitEthernet0/1
description cust1 private VRF
ip vrf forwarding cust1-vrf
ip address 192.168.88.20 255.255.255.0
!
ip route vrf internet-vrf 0.0.0.0 0.0.0.0 10.1.1.1
To remember:
- "ip vrf forwarding <ivrf>" on the tunnel interface
- "tunnel vrf <fvrf>" on the tunnel interface
- crypto keyring tagged with fvrf
- NO "vrf <ivrf>" on isakmp profile
- fvrf on match statement of isakmp profile
- no need to worry about RRI (tunnel destination needs to be reachable in fvrf), inside traffic gets routed to the tunnel interface
- interfaces in their VRF and proper routes in each VRF as well
Which scenarios are supported?
crypto map
everything except fvrf=vrf1 and ivrf=global i.e.
ivrf=fvrf=global is OK (this is normal non-vrf aware ipsec)
ivrf=fvrf=vrf1 is OK (this is the example shown in the video)
ivrf=vrf1 and fvrf=vrf2 is OK
ivrf=vrf1 and fvrf=global is OK
tunnel protection
=> everything
Troubleshooting
Tunnel establishment
- in ISAKMP debugs, scroll up and make sure that you match the expected profile!!!, don't focus too much on the errors that you see later on, if you don't match the right profile, start by verifying this.
- is the PSK in a keyring and tagged to the right VRF? Does the profile we match have the keyring?
Tunnel is up but traffic not passing
- Check the routes in each VRF
- confirm with "show ip cef vrf <ivrf> <remote-subnet-ip>" the adjacency for the remote subnet and the interface it goes to
- confirm with "show ip cef vrf <fvrf> <peer-ip>" the adjacency for the remote peer
- look for "protected vrf" in "show crypto ipsec sa", are we protecting the expected VRF?
Known bugs:
CSCtg41606
Further references
