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Foundry Configuration Guide for the FESX, FSX, and FWSX
22 - 4
© Foundry Networks, Inc.
December 2005
Virtual Router IP Address
VRRP does not use virtual IP addresses. Thus, there is no virtual IP address associated with a virtual router.
Instead, you associate the virtual router with one or more real interface IP addresses configured on the router that
owns the real IP address(es). In Figure 22.2, the virtual router with VRID1 is associated with real IP address
192.53.5.1, which is configured on interface e1/6 on Router1. VRIDs are interface-level parameters, not system-
level parameters, so the IP address you associate with the VRID must already be a real IP address configured on
the Owner’s interface.
NOTE:
You also can associate a virtual router with a virtual interface. A virtual interface is a named set of
physical interfaces.
When you configure the Backup router for the VRID, specify the same IP address as the one you specify on the
Owner. This is the IP address used by the host as its default gateway. The IP address cannot also exist on the
Backup router. The interface on which you configure the VRID on the Backup router must have an IP address in
the same sub-net.
NOTE:
If you delete a real IP address used by a VRRP entry, the VRRP entry also is deleted automatically.
NOTE:
When a Backup takes over forwarding responsibilities from a failed Master router, the Backup forwards
traffic addressed to the VRID MAC address, which the host believes is the MAC address of the router interface for
its default gateway. However, the Backup cannot reply to IP pings sent to the IP address(es) associated with the
VRID. Because the IP address(es) are owned by the Owner, if the Owner is unavailable, the IP addresses are
unavailable as packet destinations.
Master Negotiation
The routers within a VRID use the VRRP priority values associated with each router to determine which router
becomes the Master. When you configure the VRID on a router interface, you specify whether the router is the
Owner of the IP address(es) you plan to associate with the VRID or a Backup. If you indicate that the router is the
Owner of the IP address(es), the software automatically sets the router’s VRRP priority for the VRID to 255, the
highest VRRP priority. The router with the highest priority becomes the Master.
Backup routers can have a priority from 3 – 254, which you assign when you configure the VRID on the Backup
router’s interfaces. The default VRRP priority for Backup routers is 100.
Because the router that owns the IP addresses associated with the VRID always has the highest priority, when all
the routers in the virtual router are operating normally, the negotiation process results in the Owner of the VRID’s
IP address(es) becoming the Master router. Thus, the VRRP negotiation results in the normal case, in which the
hosts’ path to the default route is to the router that owns the interface for that route.
Hello Messages
VRRP routers use Hello messages for negotiation to determine the Master router. VRRP routers send Hello
messages to IP Multicast address 224.0.0.18. The frequency with which the Master sends Hello messages is the
Hello Interval. Only the Master sends Hello messages. However, a Backup uses the Hello interval you configure
for the Backup if it becomes the Master.
The Backup routers wait for a period of time called the Dead Interval for a Hello message from the Master. If a
Backup router does not receive a Hello message by the time the dead interval expires, the Backup router assumes
that the Master router is dead and negotiates with the other Backups to select a new Master router. The Backup
router with the highest priority becomes the new Master.
If the Owner becomes unavailable, but then comes back online, the Owner again becomes the Master router. The
Owner becomes the Master router again because it has the highest priority. The Owner always becomes the
Master again when the Owner comes back online.
Содержание FastIron Edge Switch X424
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