SRRP Redundancy
SRRP Diagram
Description
SRRP (Subscriber Routed Redundancy Protocol) provides active/backup redundancy for subscriber sessions between the BNG MASTER and the BNG SLAVE. Unlike VRRP which operates at layer 3, SRRP is designed specifically for ESM (Enhanced Subscriber Management) environments.
SRRP instances
The lab configures 3 SRRP instances, one for each Group Interface:
| SRRP ID | Group Interface | Service | SRRP VLAN |
|---|---|---|---|
| 1 | ipv6-only | IPv6-only + NAT64 | 4094.1 |
| 2 | dual-stack | Dual-Stack + CGNAT | 4094.2 |
| 3 | vip | VIP + One-to-One NAT | 4094.3 |
SRRP Configuration (more information at MOPT)
BNG MASTER (Priority 200)
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 admin-state enable
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 priority 200
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 message-path 1/1/c2/1:4094.1
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 keep-alive-interval 30
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 policy 1
BNG SLAVE (Priority 50)
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 admin-state enable
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 priority 50
/configure service vprn "9998" subscriber-interface "services" group-interface "ipv6-only" srrp 1 message-path 1/1/c2/1:4094.1
SRRP Message Path
SRRP messages travel over VLAN 4094 through the OLT. It is critical that the OLT has a MAC-VRF configured for VLAN 4094 that includes the ports to both BNGs:
# En OLT (SR Linux)
set /interface ethernet-1/1 subinterface 4094 type bridged
set /interface ethernet-1/1 subinterface 4094 vlan encap single-tagged vlan-id 4094
set /interface ethernet-1/2 subinterface 4094 type bridged
set /interface ethernet-1/2 subinterface 4094 vlan encap single-tagged vlan-id 4094
set /network-instance bd-srrp type mac-vrf
set /network-instance bd-srrp admin-state enable
set /network-instance bd-srrp interface ethernet-1/1.4094
set /network-instance bd-srrp interface ethernet-1/2.4094
If the OLT does not have MAC-VRF bd-srrp configured with VLAN 4094, SRRP messages will not arrive between the BNGs and both will declare MASTER simultaneously, causing IP address conflicts and session loss.
Multi-Chassis Redundancy
State synchronization between BNGs is configured via MCS (Multi-Chassis Synchronization):
/configure redundancy multi-chassis peer 10.0.0.2 admin-state enable
/configure redundancy multi-chassis peer 10.0.0.2 source-address 10.0.0.1
/configure redundancy multi-chassis peer 10.0.0.2 sync admin-state enable
/configure redundancy multi-chassis peer 10.0.0.2 sync local-dhcp-server true
/configure redundancy multi-chassis peer 10.0.0.2 sync srrp true
/configure redundancy multi-chassis peer 10.0.0.2 sync sub-host-trk true
/configure redundancy multi-chassis peer 10.0.0.2 sync sub-mgmt ipoe true
/configure redundancy multi-chassis peer 10.0.0.2 sync sub-mgmt pppoe true
/configure redundancy multi-chassis peer 10.0.0.2 sync tags port 1/1/c2/1 sync-tag "mcs"
DHCP Failover
Each DHCP pool has failover configured towards the BNG peer:
/configure service vprn "9998" dhcp-server dhcpv6 "suscriptores_v6" pool "IPv6" failover admin-state enable
/configure service vprn "9998" dhcp-server dhcpv6 "suscriptores_v6" pool "IPv6" failover ignore-mclt-on-takeover true
/configure service vprn "9998" dhcp-server dhcpv6 "suscriptores_v6" pool "IPv6" failover partner-down-delay 3600
/configure service vprn "9998" dhcp-server dhcpv6 "suscriptores_v6" pool "IPv6" failover peer 10.0.0.2 sync-tag "dhcpv6-only"
Verification
# Ver estado SRRP
show srrp
# Verificar multi-chassis
show redundancy multi-chassis all
# Ver sincronización
show redundancy multi-chassis sync peer 10.0.0.2