Subscriber Router Redundancy Protocol (SRRP) is used on the 7750 SR and 7450 ESS and is closely tied to the multi-chassis synchronization (MCS) protocol used to synchronize information between redundant nodes. An MCS peer must be configured and operational when subscriber hosts have a redundant connection to two nodes. Subscriber hosts are identified by the ingress SAP, the host’s IP and MAC addresses. After a host is identified on one node, the MCS peering is used to inform the other node that the host exists and conveys the dynamic DHCP lease state information of the host. MCS creates a common association between the virtual ports (SAPs) shared by a subscriber. This association is configured at the MCS peering level by defining a tag for a port and range of SAPs. The same tag is defined on the other nodes peering context for another port (does not need to be the same port-ID) with the same SAP range. In this manner, a subscriber host and Dot1Q tag sent across the peering with the appropriate tag is mapped to the redundant SAP on the other node.
SRRP can only be configured on group interfaces. When SRRP is active on a group IP interface, the SRRP instance attempts to communicate through in-band (over the group IP interfaces SAPs) and out-of-band (over the group IP interfaces redundant IP interface) messages to a remote router. If the remote router is also running SRRP with the same SRRP instance ID, one router enters a master state while the other router enters a backup state. Because both routers are sharing a common SRRP gateway MAC address that is used for the SRRP gateway IP addresses and for proxy ARP functions, either node may act as the default gateway for the attached subscriber hosts.
For correct operation, each subscriber subnet associated with the SRRP instance must have a gw-address defined. The SRRP instance cannot be activated (no shutdown) unless each subscriber subnet associated with the group IP interface has an SRRP gateway IP address. Once the SRRP instance is activated, new subscriber subnets cannot be added without a corresponding SRRP gateway IP address. Table: SRRP state effect on subscriber hosts associated with group IP interface describes how the SRRP instance state is used to manage access to subscriber hosts associated with the group IP interface.
SRRP instances are created in the disabled state (shutdown). To activate SRRP the no shutdown command in the SRRP context must be executed.
Before activating an SRRP instance on a group IP interface, the following actions are required:
Add a SRRP gateway IP addresses to all subscriber subnets associated with the group IP interface, including subnets on subscriber IP interfaces associated as retail routing contexts (at least one subnet must be on the subscriber IP interface containing the group IP interface and its SRRP instance).
Create a redundant IP interface and associate it with the SRRP instances group IP interface for shunting traffic to the remote router when master.
Specify the group IP interface SAP used for SRRP advertisement and Information messaging.
Before activating an SRRP instance on a group IP interface, the following actions should be considered:
Associate the SRRP instance to a Multi-Chassis Synchronization (MCS) peering terminating on the neighboring router (the MCS peering should exist as the peering is required for redundant subscriber host management).
Define a description string for the SRRP instance.
Specify the SRRP gateway MAC address used by the SRRP instance (must be the same on both the local and remote SRRP instance participating in the same SRRP context).
Change the base priority for the SRRP instance.
Specify one or more VRRP policies to dynamically manage the SRRP instance base priority.
Specify a new keep alive interval for the SRRP instance.
Table: SRRP state effect on subscriber hosts associated with group IP interface lists the SRRP’s state effect on subscriber hosts associated with group IP interfaces.
| SRRP state | ARP | Local proxy ARP enabled | Remote proxy ARP enabled | Subscriber host routing |
|---|---|---|---|---|
Disabled |
- Responds to ARP for all owned subscriber subnet IP addresses. - Will not respond to ARP for subscriber subnet SRRP gateway IP addresses. - All ARP responses contain the native MAC of the group IP interface (not the SRRP gateway MAC). |
- Responds to ARP for all subscriber hosts on the subscriber subnet. |
- Responds to ARP for all reachable remote IP hosts. |
- All routing out the group IP interface uses the native group IP interface MAC address. - The group IP interface redundant IP interface is not used. - Does not accept packets destined for the SRRP gateway MAC received on the group IP interface. |
Becoming Master (To enter becoming master state, a master must currently exist) |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Responds to ARP for subscriber subnet SRRP gateway IP addresses. (hardware address = SRRP gateway IP address, source MAC = group IP interface native MAC). |
- Responds to ARP for all subscriber hosts on the subscriber subnet (hardware address = SRRP gateway MAC address, source MAC = group IP interface native MAC). |
- Responds to ARP for all reachable remote IP hosts (hardware address = SRRP gateway MAC address, source MAC = group IP interface native MAC). |
- All routing out the group IP interface uses the native group IP interface MAC address. - Subscriber hosts mapped to the redundant IP interface are remapped to the group IP interface. - Does not accept packets destined for the SRRP gateway MAC received on the group IP interface. |
Master |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Responds to ARP for subscriber subnet SRRP gateway IP addresses (hardware address = SRRP gateway IP address, source MAC = group IP interface native MAC). |
- Responds to ARP for all subscriber hosts on the subscriber subnet (hardware address = SRRP gateway MAC address, source MAC = group IP interface native MAC). |
- Responds to ARP for all reachable remote IP hosts (hardware address = SRRP gateway MAC address, source MAC = group IP interface native MAC). |
- All routing out the group IP interface uses the SRRP gateway MAC address. - Subscriber hosts mapped to the redundant IP interface are remapped to the group IP interface. - Accepts packets destined for the SRRP gateway MAC received on the group IP interface. |
Becoming Backup (redundant IP interface operational) |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Does not respond to ARP for subscriber subnet SRRP gateway IP addresses. |
- Does not respond to ARP for any subscriber hosts on the subscriber subnet. |
- Does not respond to ARP for any remote IP hosts. |
- Does not route out the group IP interface for subscriber hosts associated with the subscriber subnet. - Accepts packets destined for the SRRP gateway MAC received on the group IP interface. - Subscriber hosts mapped to the group IP interface are remapped to the redundant IP interface. |
Becoming Backup (redundant IP interface not available) |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Does not respond to ARP for subscriber subnet SRRP gateway IP addresses. |
- Does not respond to ARP for any subscriber hosts on the subscriber subnet. |
- Does not respond to ARP for any remote IP hosts. |
- Will route out the group IP interface for subscriber hosts associated with the subscriber subnet using the group IP interface native MAC address. - Subscriber hosts mapped to the redundant IP interface are remapped to the group IP interface. - Accepts packets destined for the SRRP gateway MAC received on the group IP interface. |
Backup (redundant IP interface operational) |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Will not respond to ARP for subscriber subnet SRRP gateway IP addresses. |
- Does not respond to ARP for any subscriber hosts on the subscriber subnet. |
- Does not respond to ARP for any remote IP hosts. |
- Does not route out the group IP interface for subscriber hosts associated with the subscriber subnet. - Subscriber hosts mapped to the group IP interface are remapped to the redundant IP interface. - Does not accept packets destined for the SRRP gateway MAC received on the group IP interface. |
Backup (redundant IP interface not available) |
- Responds to ARP for all owned subscriber subnet IP addresses (hardware address and source MAC = group IP interface native MAC). - Does not respond to ARP for subscriber subnet SRRP gateway IP addresses. |
- Does not respond to ARP for any subscriber hosts on the subscriber subnet. |
- Does not respond to ARP for any remote IP hosts. |
- Routes out the group IP interface for subscriber hosts associated with the subscriber subnet using the group IP interface native MAC address. - Subscriber hosts mapped to the redundant IP interface are remapped to the group IP interface. - Does not accept packets destined for the SRRP gateway MAC received on the group IP interface. |