Manual:Virtual Routing and Forwarding

Preliminary version - will be expanded!

Description

New routing-test package in version 3.x allows to create multiple Virtual Routing and Forwarding instances on a single router. This is useful for BGP based MPLS VPNs. Unlike MPLS BGP VPLS, which is OSI Layer 2 technology, BGP VPNs works in Layer 3 and as such exchanges IP prefixes between routers. VRFs solves the problem of overlapping IP prefixes, and provides the required privacy (via separated routing for different VPNs).

To create a VRF, configure it under /ip route vrf. You can now add routes to that VRF - simply specify routing-mark attribute. Connected routes from interfaces belonging to a VRF will be installed in right routing table automatically.

Technically VRFs are based on policy routing. There is exactly one policy routing table for each active VRF. Note that existing policy routing support will not be changed, but you will not be able to have policy routing within a VRF. The main difference between VRF tables and simple policy routing is that routes in VRF tables resolve nexthops in their own routing table by default, while policy routes always use main routing table. Read-only route attribute gateway-table displays information about which table is used for a particular route (default is main).

The real fun begins when you start to configure BGP. You can use multiprotocol BGP to distribute those routes - not only to other routers, but also to different routing tables in the router itself. Route installation in VRF tables is controlled by BGP extended communities attribute. Configure import and export lists under /ip route vrf, import-route-target and export-route-target. Export route target list for a VRF should contained at least the route distinguisher for that VRF.

Active multiprotocol BGP routes are installed in a separate routing table, which can be observed at /routing bgp vpnv4-route. These so called VPNv4 routes has prefix that consists of route-distinguisher and an IPv4 route prefix. This way you can have overlapping IPv4 prefixes distributed in BGP. route-distinguisher can be configured under /ip route vrf. Usually there will be one-to-one correspondence between route-distinguishers and VRFs, but that's not a mandatory requirement.

Please note that a VPNv4 route will be distributed only if it has a valid MPLS label. You need to install mpls or mpls-test package and configure valid label range (default is OK) for this to work.

An example with Cisco

In this example we create two VPNs for cust-one and cust-two, and exchange all routes between them.

Configuration

Mikrotik:

Addresses are like this:

[admin@MikroTik] > /ip address p
Flags: X - disabled, I - invalid, D - dynamic
 #   ADDRESS            NETWORK         BROADCAST       INTERFACE
 0   10.0.0.131/24      10.0.0.0        10.0.0.255      ether1
 1   1.1.1.1/24         1.1.1.0         1.1.1.255       ether2

Add default route:

/ip route add gateway=10.0.0.1

Configure VRFs:

/ip route vrf add interfaces=ether2 route-distinguisher=1.1.1.1:111 export-route-targets=1.1.1.1:111 \
   import-route-targets=1.1.1.1:111,2.2.2.2:222 routing-mark=cust-one
 
/ip route vrf add interfaces=ether3 route-distinguisher=2.2.2.2:222 export-route-targets=2.2.2.2:222 \
   import-route-targets=1.1.1.1:111,2.2.2.2:222 routing-mark=cust-two

Configure VPNv4 redistribution and multiprotocol BGP:

/routing bgp instance set default as=64550 redistribute-connected=yes vrf=cust-one,cust-two
/routing bgp peer add remote-address=10.0.11.202 remote-as=64550 instance=default address-families=vpnv4

Cisco: (note that VRF names are not important, they are the same on both MT and Cisco only by convention)

interface FastEthernet0/0
 ip address 10.0.11.202 255.255.255.0
 
ip vrf cust-one
 rd 1.1.1.1:111
 route-target export 1.1.1.1:111
 route-target import 1.1.1.1:111
 route-target import 2.2.2.2:222
 exit
 
ip vrf cust-two
 rd 2.2.2.2:222
 route-target export 2.2.2.2:222
 route-target import 1.1.1.1:111
 route-target import 2.2.2.2:222
 exit
 
interface Tunnel1
 ip vrf forwarding cust-one
 ip address 2.2.2.2 255.255.255.0
 tunnel source 10.0.11.202
 tunnel destination X.X.X.X
 
interface Tunnel2
 ip vrf forwarding cust-two
 ip address 3.3.3.3 255.255.255.0
 tunnel source 10.0.11.202
 tunnel destination Y.Y.Y.Y
 
router bgp 64550
 neighbor 10.0.0.131 remote-as 64550
 address-family vpnv4
  neighbor 10.0.0.131 activate
  neighbor 10.0.0.131 send-community both
  exit-address-family
 address-family ipv4 vrf cust-one
  redistribute connected
  exit-address-family
 address-family ipv4 vrf cust-two
  redistribute connected
  exit-address-family

Results

Cisco

VPNv4 routing table:

C7200#show ip bgp vpnv4 all
BGP table version is 20, local router ID is 10.0.11.202
Status codes: s suppressed, d damped, h history, * valid, > best, i - internal,
              r RIB-failure, S Stale
Origin codes: i - IGP, e - EGP, ? - incomplete
   Network          Next Hop            Metric LocPrf Weight Path
Route Distinguisher: 1.1.1.1:111 (default for vrf cust-one)
*>i1.1.1.0/24       10.0.0.131                    100      0 ?
*> 2.2.2.0/24       0.0.0.0                  0         32768 ?
*> 3.3.3.0/24       0.0.0.0                  0         32768 ?
Route Distinguisher: 2.2.2.2:222 (default for vrf cust-two)
*>i1.1.1.0/24       10.0.0.131                    100      0 ?
*> 2.2.2.0/24       0.0.0.0                  0         32768 ?
*> 3.3.3.0/24       0.0.0.0                  0         32768 ?

Routing table for customer one:

C7200#show ip route vrf cust-one
Routing Table: cust-one
Codes: C - connected, S - static, R - RIP, M - mobile, B - BGP
      D - EIGRP, EX - EIGRP external, O - OSPF, IA - OSPF inter area
      N1 - OSPF NSSA external type 1, N2 - OSPF NSSA external type 2
      E1 - OSPF external type 1, E2 - OSPF external type 2
      i - IS-IS, su - IS-IS summary, L1 - IS-IS level-1, L2 - IS-IS level-2
      ia - IS-IS inter area, * - candidate default, U - per-user static route
      o - ODR, P - periodic downloaded static route
Gateway of last resort is not set
    1.0.0.0/24 is subnetted, 1 subnets
B       1.1.1.0 [200/0] via 10.0.0.131, 00:02:51
    2.0.0.0/24 is subnetted, 1 subnets
C       2.2.2.0 is directly connected, Tunnel1
    3.0.0.0/24 is subnetted, 1 subnets
B       3.3.3.0 is directly connected, 00:01:20, Tunnel2

Mikrotik

VPNv4 routing table:

[admin@MikroTik] > vpnv4-route print detail
Flags: N - no label
 0   route-distinguisher=1.1.1.1:111 dst-address=2.2.2.0/24 gateway=10.0.11.202
     interface=ether1 in-label=17 out-label=16 bgp-local-pref=100 bgp-med=0
     bgp-origin=incomplete bgp-ext-communities="RT:1.1.1.1:111"
 
 1   route-distinguisher=2.2.2.2:222 dst-address=3.3.3.0/24 gateway=10.0.11.202
     interface=ether1 in-label=18 out-label=17 bgp-local-pref=100 bgp-med=0
     bgp-origin=incomplete bgp-ext-communities="RT:2.2.2.2:222"
 
 2   route-distinguisher=1.1.1.1:111 dst-address=1.1.1.0/24 interface=ether2
     in-label=16 bgp-ext-communities="RT:1.1.1.1:111"

All IP routing tables:

[admin@MikroTik] > /ip route p detail
Flags: X - disabled, A - active, D - dynamic,
C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme,
B - blackhole, U - unreachable, P - prohibit
  
 # ---------------------- routes for customer 1 --------------------------
 # a connected route that is bound to a particular VRF
 0 ADC  dst-address=1.1.1.0/24 pref-src=1.1.1.1 interface=ether2 distance=0 scope=10
        routing-mark=cust-one
  
 # this route is received from Cisco and imported to customer's 1 VRF
 1 ADb  dst-address=2.2.2.0/24 gateway=10.0.11.202 interface=ether1 gateway-table=main
        gateway-state=recursive distance=20 scope=40 target-scope=30
        routing-mark=cust-one bgp-local-pref=100 bgp-med=0 bgp-origin=incomplete
        bgp-ext-communities="RT:1.1.1.1:111"
  
 # from Cisco
 2 ADb  dst-address=3.3.3.0/24 gateway=10.0.11.202 interface=ether1 gateway-table=main
        gateway-state=recursive distance=20 scope=40 target-scope=30
        routing-mark=cust-one bgp-local-pref=100 bgp-med=0 bgp-origin=incomplete
        bgp-ext-communities="RT:2.2.2.2:222"
  
 # ---------------------- routes for customer 2 --------------------------
 # "locally" reimported via bgp to a different table
 3 ADb  dst-address=1.1.1.0/24 distance=20 routing-mark=cust-two
        bgp-ext-communities="RT:1.1.1.1:111"
  
 # from Cisco and imported to customer's 2 VRF
 4 ADb  dst-address=2.2.2.0/24 gateway=10.0.11.202 interface=ether1 gateway-table=main
        gateway-state=recursive distance=20 scope=40 target-scope=30
        routing-mark=cust-two bgp-local-pref=100 bgp-med=0 bgp-origin=incomplete
        bgp-ext-communities="RT:1.1.1.1:111"
  
 # from Cisco
 5 ADb  dst-address=3.3.3.0/24 gateway=10.0.11.202 interface=ether1 gateway-table=main
        gateway-state=recursive distance=20 scope=40 target-scope=30
        routing-mark=cust-two bgp-local-pref=100 bgp-med=0 bgp-origin=incomplete
        bgp-ext-communities="RT:2.2.2.2:222"
  
 # ------------------------- "main" table ------------------------------
 6 A S  dst-address=0.0.0.0/0 gateway=10.0.0.1 interface=ether1 gateway-table=main
        gateway-state=reachable distance=1 scope=30 target-scope=10
 
 7 ADC  dst-address=10.0.0.0/24 pref-src=10.0.0.131 interface=ether1 distance=0
        scope=10

References

RFC 4364: BGP/MPLS IP Virtual Private Networks (VPNs)

MPLS Fundamentals, chapter 7, Luc De Ghein, Cisco Press 2006