Layer 3 - amybuck/SONiC-NAS GitHub Wiki
The SONiC NAS Host-Adapter supports unicast routing over Linux interfaces using routes in the Linux kernel routing table. Applications can also use the SONiC Object Library API to configure routes. This information describes how to configure Layer 3 unicast routing to provision the NPU.
The SONiC NAS Host-Adapter routing subsystem manages the forwarding information base (FIB). The routing subsystem programs routes with resolved next-hops using ARP/Neighbor table entries received from the Linux kernel.
IPv4 Routing
A routing table entry consists of a destination IP address prefix and at least one next-hop address or a Linux interface.
$ ip route show
default dev eth0 scope link
3.3.3.0/24 dev e101-003-0 proto kernel scope link src 3.3.3.1
$ ip route add 11.10.10.0/24 dev e101-003-0
$ ip route show
default dev eth0 scope link
3.3.3.0/24 dev e101-003-0 proto kernel scope link src 3.3.3.1
11.10.10.0/24 dev e101-003-0 scope link
Configure Static Route with Next-Hop
$ ip route add 30.30.30.0/24 via 3.3.3.3
$ ip route show
default dev eth0 scope link
3.3.3.0/24 dev e101-003-0 proto kernel scope link src 3.3.3.1
30.30.30.0/24 via 3.3.3.3 dev e101-003-0
Delete Static Route
$ ip route delete 11.10.10.0/24
$ ip route show
default dev eth0 scope link
3.3.3.0/24 dev e101-003-0 proto kernel scope link src 3.3.3.1
To add a persistent static route that is saved after a reboot, configure the route in the /etc/network/interfaces file. See IP Route Tools for information about how to configure Linux routing.
IPv6 Routing
You can add, delete, or modify the IPv6 routes and next hops in the IPv6 routing table.
$ ip -6 route add 5::5/64 via 3::3
$ ip -6 route show
3::/64 dev e101-003-0 proto kernel metric 256
5::/64 via 3::3 dev e101-003-0 metric 1024
Debug and Troubleshoot IPv6 Routing
$ ip monitor
30.30.30.0/24 via 3.3.3.3 dev e00-3
3::/64 via 3::3 dev e101-003-0 metric 1024
5::/64 via 3::3 dev e101-003-0 metric 1024
ARP and Neighbor Tables
SONiC uses ARP and Neighbor table entries to resolve adjacencies by using the host IP address-to-MAC address binding. In Linux, the ARP table is used for IPv4 routing; the Neighbor table is used for IPv6 routing.
Configure and View Kernel ARP Table Entries
$ arp -n
Address HWtype HWaddress Flags Mask Iface 3.3.3.4 ether 90:b1:1c:f4:9d:44 C
Configure IPv6 Address
$ ifconfig e101-003-0 inet6 add 3::1/64
$ ifconfig e101-003-0
e101-003-0 Link encap:Ethernet HWaddr 90:b1:1c:f4:a8:ea
inet addr:3.3.3.1 Bcast:3.3.3.255 Mask:255.255.255.0
inet6 addr: 3::1/64 Scope:Global
inet6 addr: fe80::92b1:1cff:fef4:a8ea/64 Scope:Link
UP BROADCAST RUNNING MULTICAST MTU:1500 Metric:1
RX packets:532 errors:0 dropped:0 overruns:0 frame:0
TX packets:173 errors:0 dropped:0 overruns:0 carrier:0
collisions:0 txqueuelen:500
RX bytes:46451 (45.3 KiB) TX bytes:25650 (25.0 KiB)
Display IPv6 Neighbor Table
$ ip -6 neighbor show
3::3 dev e101-003-0 lladdr 90:b1:1c:f4:9d:44 router REACHABLE
Ping IPv6 Neighbor
$ ping6 3::3
PING 3::3(3::3) 56 data bytes
64 bytes from 3::3: icmp_seq=1 ttl=64 time=1.74 ms
$ tcpdump -i e101-003-0
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on e101-003-0, link-type EN10MB (Ethernet), capture size 262144 bytes
04:30:17.053115 IP6 3::1 > 3::3: ICMP6, echo request, seq 8, length 64
Equal Cost Multi-Path (ECMP)
The Linux networking stack supports ECMP by adding multiple next-hops to the route.
Configure ECMP Route
$ ip route add 40.40.40.0/24 nexthop via 3.3.3.6 nexthop via 4.4.4.7
$ ip route show
default dev eth0 scope link
3.3.3.0/24 dev e101-003-0 proto kernel scope link src 3.3.3.1
40.40.40.0/24
nexthop via 3.3.3.6 dev e101-003-0 weight 1
nexthop via 4.4.4.7 dev e101-004-0 weight 1
NOTE: The Linux kernel provides limited support for IPv6 multi-path routing.
Layer 3 Routing Topology Example
When you configure an IP address, use any Linux utility command such as ip addr add or ifconfig to configure an interface.
Configure IP Address on R1
$ ip addr add 10.1.1.1/24 dev e101-007-0
$ ip addr add 11.1.1.1/24 dev e101-001-0
Configure IP Address on R2
$ ip addr add 10.1.1.2/24 dev e101-007-0
$ ip addr add 12.1.1.1/24 dev e101-001-0
Verify IP Address Configuration on R1
$ ip addr show e101-007-0
16: e101-007-0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group
default qlen 500
link/ether 74:e6:e2:f6:af:87 brd ff:ff:ff:ff:ff:ff
inet 10.1.1.1/24 scope global e101-007-0
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef6:af87/64 scope link
valid_lft forever preferred_lft forever
$ ip addr show e101-001-0
10: e101-001-0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group
default qlen 500
link/ether 74:e6:e2:f6:af:81 brd ff:ff:ff:ff:ff:ff
inet 11.1.1.1/24 scope global e101-001-0
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef6:af81/64 scope link
valid_lft forever preferred_lft forever
Verify IP Address Configuration on R2
$ ip addr show e101-007-0
16: e101-007-0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group
default qlen 500
link/ether 74:e6:e2:f6:ba:87 brd ff:ff:ff:ff:ff:ff
inet 10.1.1.2/24 scope global e101-007-0
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef6:ba87/64 scope link
valid_lft forever preferred_lft forever
$ ip addr show e101-001-0
10: e101-001-0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq state UP group
default qlen 500
link/ether 74:e6:e2:f6:ba:81 brd ff:ff:ff:ff:ff:ff
inet 12.1.1.1/24 scope global e101-001-0
valid_lft forever preferred_lft forever
inet6 fe80::76e6:e2ff:fef6:ba81/64 scope link
valid_lft forever preferred_lft forever
Enable Interfaces on R1 and R2
$ ip link set dev e101-007-0 up
$ ip link set dev e101-001-0 up
Configure Static Route to Server on R1
$ ip route add 12.1.1.0/24 via 10.1.1.2
Configure Static Route to Server on R2
$ ip route add 11.1.1.0/24 via 10.1.1.1
Ping Neighbor Route and Server (Server 2) from R1
$ ping 11.1.1.2
View ARP Table on R1
$ arp -n
Address HWtype HWaddress Flags Mask Iface
11.1.1.2 ether 00:00:00:1d:9a:bd C e101-001-0
10.1.1.2 ether 74:e6:e2:f6:ba:87 C e101-007-0
View ARP Table on R2
$ arp -n
Address HWtype HWaddress Flags Mask Iface
10.1.1.1 ether 74:e6:e2:f6:af:87 C e101-007-0
12.1.1.2 ether 00:00:00:1d:9a:be C e101-001-0
See SONiC Object Library Application Examples for information about how to program routes using the SONiC Object Library API.
Dynamic Routing
To enable dynamic routing, configure BGP and OSPF using open-source routing stacks, such as Quagga, Bird, and other third-party applications.