Installation and Getting Started Guide
For example, an HP routing switch running OSPF and RIP can pass a route learned through RIP to OSPF. The
router associates a metric and other parameters with a route when the router redistributes the route to other
protocols. You can modify these parameters and permit or deny routes from being distributed using route
You define the filters for each of the protocols that redistributes the routes. For example, if you want to control
how the routing switch redistributes routes learned through RIP to OSPF, you use IP/RIP commands or Web
management screens to define the filters.
User Datagram Protocol (UDP) Helper
HP routing switches can relay UDP packets to their destination for a specific application even when the
destination server is not on the local LAN segment. For example, an HP routing switch can relay UDP packets for
the following applications to their destination nodes: bootps, domain, and tftp. This feature is especially useful for
configuring the HP routing switch to help DHCP packets reach their intended server and client.
For details on UDP helper and its configuration, see the "Configuring IP" chapter in the Advanced Configuration
and Management Guide.
NOTE: UDP Helper is supported only on HP routing switches. To configure an HP switch to help BootP/DHCP
packets, use the DHCP Assist feature. See the "Configuring IP" chapter in the Advanced Configuration and
TCP/UDP Access Policies
TCP/UDP access policies (sometimes called session filters) allow you to filter packets for specific Layer 4
sessions. For example, you can use session filters to prohibit specific users from using TCP port 80 (HTTP for
web traffic). All HP devices support TCP/UDP access policies. For syntax information, see the "Policies and
Filters" chapter in the Advanced Configuration and Management Guide.
The following sections describe the redundancy features listed in Table 7.1 on page 7-1.
Virtual Router Redundancy Protocol (VRRP)
The Virtual Router Redundancy Protocol (VRRP), described in RFC 2338, allows routing switches and even
third-party routers to be configured together as a virtual router. Generally, a host configured to use a default router
will lose its connection to the rest of the network if the default router becomes unavailable. However, if you
configure several routers as a VRRP virtual router, and then use the virtual router as the default router for the
hosts, the hosts receive uninterrupted service even if one of the routers within the virtual router becomes
One of the routers in the virtual router is the "active" or "master" router and handles the traffic sent to the virtual
router's MAC address or IP address. The other routers remain in standby mode while the active router is
If the active router becomes unavailable, one of the standby routers becomes the new active router. The new
active router uses the same virtual MAC address and virtual IP address as the previous master, so hosts are
unaware that a router has become unavailable. As far as the hosts are concerned, the MAC address and IP
address of the virtual router is still alive. You can fix the link or router problem off-line while network service
In addition to the standard redundancy support described in RFC 2338, HP's implementation of VRRP enables
you to track the status of both the in and out ports for host traffic. The track port feature ensures that if an out port
goes down, even if the in port is still up, VRRP lowers the router priority and thus causes a renegotiation for the
VRRPE is an HP enhancement to standard VRRP.
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