Cisco XR 12000 Specifications download pdf (Page 50)

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Cisco XR 12000 Series Router SIP and SPA Software Configuration Guide, Release 3.2

Release 3.2, OL-6396-01, Rev.A1 January 9, 2006

Chapter 4 Configuring Ethernet SPAs on Cisco IOS XR Software

Configuration Tasks

MAC Address

A MAC address is a 6-byte-long hardware address that uniquely identifies each node of a network.

802.1Q VLAN

A VLAN is a group of devices on one or more LANs that are configured so that they can communicate

as if they were attached to the same wire, when in fact they are located on a number of different LAN

segments. Because VLANs are based on logical instead of physical connections, it is very flexible for

user and host management, bandwidth allocation, and resource optimization.

The IEEE’s 802.1Q protocol standard addresses the problem of breaking large networks into smaller

parts so broadcast and multicast traffic does not consume more bandwidth than necessary. The standard

also helps provide a higher level of security between segments of internal networks.

The 802.1Q specification establishes a standard method for inserting VLAN membership information

into Ethernet frames.

VRRP

The Virtual Router Redundancy Protocol (VRRP) eliminates the single point of failure inherent in the

static default routed environment. VRRP specifies an election protocol that dynamically assigns

responsibility for a virtual router to one of the VPN concentrators on a LAN. The VRRP VPN

concentrator controlling the IP addresses associated with a virtual router is called the Master, and

forwards packets sent to those IP addresses. When the master becomes unavailable, a backup VPN

concentrator takes the place of the master.

For more information on VRRP, refer to the “Implementing VRRP on Cisco IOS XR Software” module

of the Cisco IOS XR IP Addresses and Services Configuration Guide.

HSRP

Hot Standby Routing Protocol (HSRP) is a proprietary protocol from Cisco. HSRP is a routing protocol

that provides backup to a router in the event of failure. Several routers are connected to the same segment

of an Ethernet, FDDI, or token-ring network and work together to present the appearance of a single

virtual router on the LAN. The routers share the same IP and MAC addresses and therefore, in the event

of failure of one router, the hosts on the LAN are able to continue forwarding packets to a consistent IP

and MAC address. The transfer of routing responsibilities from one device to another is transparent to

the user.

HSRP is designed to support non disruptive failover of IP traffic in certain circumstances and to allow

hosts to appear to use a single router and to maintain connectivity even if the actual first hop router they

are using fails. In other words, HSRP protects against the failure of the first hop router when the source

host cannot learn the IP address of the first hop router dynamically. Multiple routers participate in HSRP

and in concert create the illusion of a single virtual router. HSRP ensures that one and only one of the

routers is forwarding packets on behalf of the virtual router. End hosts forward their packets to the virtual

router.

The router forwarding packets is known as the active router. A standby router is selected to replace the

active router should it fail. HSRP provides a mechanism for determining active and standby routers,

using the IP addresses on the participating routers. If an active router fails a standby router can take over

without a major interruption in the host's connectivity.

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