Driver that supports multiple loopbacks in Linux system

This driver is adding more loopback interfaces in the Linux systems. When you are using your Linux system as a router you will face the necessity to add more loopback interfaces. By default Linux offers only one loopback interface, lo.

When you are adding a new VRF in the system:

ip link add VPN type vrf table 2

It will create an interface called VPN and it can be used as loopback for that VRF. Then you can bind interfaces under this VRF and all the traffic will be forwarded into table 10.

But there are situations that you need one or more loopbacks in the default VRF of in other VRF. For example is a loopback for OSPF and another loopback to be used in BGP connections or just to be used as a route test distribution or to bind some services like SSH on that loopback.

The dummy driver can be used as an addtional loopback, but is failing if you are using it as a source or if you are trying to ping the IP of the dummy interface which resides in a VRF.

Let's take this example:

ip link add internet type vrf table 2
ip link set internet up
ip route add blackhole default metric 4278198272 table 2

We just created a new VRF called internet using the forwarding table 2.

Then let's add some dummy interfaces:

ip link add lo0 type dummy
ip link set lo0 up

ip link add lo1 type dummy
ip link set lo1 master internet
ip link set lo1 up

Then we will create some route-leaks between default VRF (called also GRT - Global Routing Table) and this VRF internet using FRRouting VPN MP-BGP. Keep in mind that we are doing route-leak using VPN BGP, not just simple BGP VRF route-leak. There are two different methods to achive this using FRR BGP. My setup is used for more complex setups to be able to export via MPLS and MP-BGP the VRFs to other routers in the network, for this reason I'm using VPN local route-leak.

Example of FRRouting BGP VPN route-leak:

frr defaults traditional
hostname RouterFW
log syslog informational
ip forwarding
ipv6 forwarding
service integrated-vtysh-config
!
interface lo
 ip address 10.0.0.1/32
exit
!
interface lo0
 ip address 10.0.0.2/32
exit
!
interface internet
 ip address 10.2.0.1/32
exit
!
interface lo1
 ip address 10.2.0.2/32
exit
!
router bgp 65500
 bgp router-id 10.0.0.1
 !
 address-family ipv4 unicast
  redistribute connected route-map VPN-GRT-connected
  rd vpn export 65500:11000
  rt vpn import 65500:11100 65500:10000 65500:10100
  rt vpn export 65500:11000
  export vpn
  import vpn
 exit-address-family
exit
!
router bgp 65500 vrf internet
 bgp router-id 10.2.0.1
 !
 address-family ipv4 unicast
  redistribute connected route-map VPN-internet-connected
  rd vpn export 65500:10000
  rt vpn import 65500:10000 65500:10100 65500:11100
  rt vpn export 65500:10000
  export vpn
  import vpn
 exit-address-family
exit
!
route-map VPN-internet-connected permit 1000
 set extcommunity rt 65500:10100
exit
!
route-map VPN-GRT-connected permit 1000
 set extcommunity rt 65500:11100
exit

Short explanation:

1. router bgp 65500 -> address-family ipv4 unicast is exporting the default VRF to VPN with extcommunity 65500:11000 and importing VPN to VRF routes with extcommunity 65500:11100 65500:10000 65500:10100.
2. We will apply extcommunity 65500:11100 to all connected routes that are redistributed in BGP table in default VRF.
3. router bgp 65500 vrf internet -> address-family ipv4 unicast is exporting the default VRF to VPN with extcommunity 65500:10100 and importing VPN to VRF routes with extcommunity 65500:10000 65500:10100 65500:11100.
4. We will apply extcommunity 65500:10100 to all connected routes that are redistributed in BGP table in default VRF. So default will import all connected routes from VRF internet and internet VRF will import all connected routes from default.

Then we should be able to see this output:

# show ip route
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
       f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

K>* 0.0.0.0/0 [0/0] via 89.X.X.193, eth0 onlink, 00:35:45
C>* 10.0.0.1/32 is directly connected, lo, 00:34:46
C>* 10.0.0.2/32 is directly connected, lo0, 00:29:40
B>* 10.2.0.1/32 [20/0] is directly connected, internet (vrf internet), weight 1, 00:29:26
B>* 10.2.0.2/32 [20/0] is directly connected, lo1 (vrf internet), weight 1, 00:29:17
C>* 89.X.X.192/26 is directly connected, eth0, 00:35:45

# show ip route vrf internet
Codes: K - kernel route, C - connected, S - static, R - RIP,
       O - OSPF, I - IS-IS, B - BGP, E - EIGRP, N - NHRP,
       T - Table, v - VNC, V - VNC-Direct, A - Babel, F - PBR,
       f - OpenFabric,
       > - selected route, * - FIB route, q - queued, r - rejected, b - backup
       t - trapped, o - offload failure

VRF internet:
K>* 0.0.0.0/0 [255/8192] unreachable (blackhole), 00:11:45
B>* 10.0.0.1/32 [20/0] is directly connected, lo (vrf default), weight 1, 00:32:54
B>* 10.0.0.2/32 [20/0] is directly connected, lo0 (vrf default), weight 1, 00:30:05
C>* 10.2.0.1/32 is directly connected, internet, 00:29:52
C>* 10.2.0.2/32 is directly connected, lo1, 00:29:42
B>* 89.X.X.192/26 [20/0] is directly connected, eth0 (vrf default), weight 1, 00:32:54

As you can see the default / GRT (Global Routing Table) routes are visible in internet VRF and vice-versa. So if we will ping the IP addresses of lo and internet interfaces it should work.

# ping -c 1 10.2.0.1 -I 10.0.0.1
PING 10.2.0.1 (10.2.0.1) from 10.0.0.1 : 56(84) bytes of data.
64 bytes from 10.2.0.1: icmp_seq=1 ttl=64 time=0.054 ms

--- 10.2.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.054/0.054/0.054/0.000 ms

# ip vrf exec internet ping 10.0.0.1 -I 10.2.0.1 -c 1
PING 10.0.0.1 (10.0.0.1) from 10.2.0.1 : 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=0.037 ms

--- 10.0.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.037/0.037/0.037/0.000 ms

Also is working if I'm using as source dummy interface lo0 from default VRF to any address in VRF:

# ping -c 1 10.2.0.1 -I 10.0.0.1
PING 10.2.0.1 (10.2.0.1) from 10.0.0.1 : 56(84) bytes of data.
64 bytes from 10.2.0.1: icmp_seq=1 ttl=64 time=0.071 ms

--- 10.2.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.071/0.071/0.071/0.000 ms

# ping -c 1 10.2.0.1 -I 10.0.0.2
PING 10.2.0.1 (10.2.0.1) from 10.0.0.2 : 56(84) bytes of data.
64 bytes from 10.2.0.1: icmp_seq=1 ttl=64 time=0.049 ms

--- 10.2.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.049/0.049/0.049/0.000 ms

But if I'm trying to ping from the dummy interface in VRF from anything in default VRF not working anymore:

# ping -c 1 10.2.0.2 -I 10.0.0.1 -w 1
PING 10.2.0.2 (10.2.0.2) from 10.0.0.1 : 56(84) bytes of data.

--- 10.2.0.2 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

# ping -c 1 10.2.0.2 -I 10.0.0.2 -w 1
PING 10.2.0.2 (10.2.0.2) from 10.0.0.2 : 56(84) bytes of data.

--- 10.2.0.2 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

Also if we are trying to use as source for the dummy interface from VRF internet and ping anything in default vrf is not working:

# ip vrf exec internet ping 10.0.0.1 -I 10.2.0.2 -c 1 -w 1
PING 10.0.0.1 (10.0.0.1) from 10.2.0.2 : 56(84) bytes of data.

--- 10.0.0.1 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

# ip vrf exec internet ping 10.0.0.2 -I 10.2.0.2 -c 1 -w 1
PING 10.0.0.2 (10.0.0.2) from 10.2.0.2 : 56(84) bytes of data.

--- 10.0.0.2 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

# ip vrf exec internet ping 89.X.X.252 -I 10.2.0.2 -c 1 -w 1
PING 89.X.X.252 (89.X.X.252) from 10.2.0.2 : 56(84) bytes of data.

--- 89.X.X.252 ping statistics ---
1 packets transmitted, 0 received, 100% packet loss, time 0ms

Adding this driver, based on dummy interface combined with VRF interface we will be able to use it as a normal loopback.

First detele the old interfaces loX:

ip link del lo1
ip link del lo0

Build this driver:

git clone https://github.com/EasyNetDev/linux-multi-loopback
cd linux-multi-loopback
make
insmod lo.ko numloopbacks=4

You will have 4 loopbacks called lo0, lo1, lo2 and lo3:

26: lo0: <NOARP,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 76:77:30:25:d8:40 brd ff:ff:ff:ff:ff:ff
27: lo1: <NOARP,UP,LOWER_UP> mtu 65536 qdisc noqueue master internet state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether 56:64:44:43:3c:04 brd ff:ff:ff:ff:ff:ff
28: lo2: <NOARP,UP,LOWER_UP> mtu 65536 qdisc noqueue master internet state UNKNOWN mode DEFAULT group default qlen 1000
    link/ether ca:14:15:a2:af:24 brd ff:ff:ff:ff:ff:ff
29: lo3: <NOARP> mtu 65536 qdisc noop state DOWN mode DEFAULT group default qlen 1000
    link/ether ee:e1:4c:89:de:2a brd ff:ff:ff:ff:ff:ff

Let's move lo1 in the internet vrf:

ip link set lo1 master internet

Let's do the test pings which failed previously:

# ping 10.2.0.2 -I 10.0.0.1 -c 1 -w 1
PING 10.2.0.2 (10.2.0.2) from 10.0.0.1 : 56(84) bytes of data.
64 bytes from 10.2.0.2: icmp_seq=1 ttl=64 time=0.048 ms

--- 10.2.0.2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.048/0.048/0.048/0.000 ms

# ping 10.2.0.2 -I 10.0.0.2 -c 1 -w 1
PING 10.2.0.2 (10.2.0.2) from 10.0.0.2 : 56(84) bytes of data.
64 bytes from 10.2.0.2: icmp_seq=1 ttl=64 time=0.043 ms

--- 10.2.0.2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.043/0.043/0.043/0.000 ms

Then from the vrf internet:

# ip vrf exec internet ping 89.X.X.252 -I 10.2.0.2 -c 1 -w 1
ping: 89.X.X.252: Name or service not known
root@RouterFW:/opt/devel/frrouting# ip vrf exec internet ping 10.0.0.1 -I 10.2.0.2 -c 1 -w 1
PING 10.0.0.1 (10.0.0.1) from 10.2.0.2 : 56(84) bytes of data.
64 bytes from 10.0.0.1: icmp_seq=1 ttl=64 time=0.062 ms

--- 10.0.0.1 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.062/0.062/0.062/0.000 ms
root@RouterFW:/opt/devel/frrouting# ip vrf exec internet ping 10.0.0.2 -I 10.2.0.2 -c 1 -w 1
PING 10.0.0.2 (10.0.0.2) from 10.2.0.2 : 56(84) bytes of data.
64 bytes from 10.0.0.2: icmp_seq=1 ttl=64 time=0.046 ms

--- 10.0.0.2 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.046/0.046/0.046/0.000 ms
root@RouterFW:/opt/devel/frrouting# ip vrf exec internet ping 89.X.X.252 -I 10.2.0.2 -c 1 -w 1
PING 89.X.X.252 (89.X.X.252) from 10.2.0.2 : 56(84) bytes of data.
64 bytes from 89.X.X.252: icmp_seq=1 ttl=64 time=0.045 ms

--- 89.X.X.252 ping statistics ---
1 packets transmitted, 1 received, 0% packet loss, time 0ms
rtt min/avg/max/mdev = 0.045/0.045/0.045/0.000 ms

THAT'S IT! Is working!!