User guide

New and Changed Information
22
Release Notes for Cisco 2500 Series for Cisco IOS Release 12.0 T
78-5563-07 Rev.H0
DNS-Based X.25 Routing
Managing a large TCP/IP network requires accurate and up-to-date maintenance of IP addresses and
X.121 address mapping information on each router database in the network. Currently, this data is
managed manually. Because these addresses are constantly being added and removed in the network,
the routing table of every router frequently needs to be updated, which is a time-consuming and
error-prone task.
X.25 has long operated over an IP network, specifically using Transmission Control Protocol (TCP) as
a reliable transport mechanism. This method is known as X.25 over TCP (XOT). However, large
networks and financial legacy environments experienced problems with the amount of route
configuration that needed to be performed manually because each router switching calls over TCP
needed every destination configured. Every destination from the host router needed a static IP route
statement, and for larger environments, these destinations could be as much as several thousand per
router. Until now, the only way to map X.121 addresses and IP addresses was on a one-to-one basis
using the x25 route x121address xot ipaddress command.
The solution to this problem was to centralize route configuration that routers could then access for their
connectivity needs. This centralization is the function of the DNS-Based X.25 Routing feature, because
the DNS server is a database of all domains and addresses on a network.
DSLw+ Ethernet Redundancy
The DLSw+ Ethernet Redundancy feature provides redundancy in an Ethernet environment. It enables
DLSw+ to support parallel paths between two points in an Ethernet environment, ensuring resiliency in
the case of a router failure and providing load balancing for traffic load.
DLSw+ could provide redundancy prior to this feature in a Token Ring environment or via backup
peers. When an end station on an Ethernet LAN had multiple active paths into a DLSw+ network,
problems occurred.
Redundancy is not possible in an Ethernet environment because, unlike Token Ring, it does not have a
RIF field in its packet. The RIF notifies a router of the path a packet has traveled by tracking each ring
number and bridge it travels along a path. If a bridge notices that the next ring matches a ring already
in the RIF, then the frame is not copied on to that ring. The RIF prevents unreliable local reachability
information, circuit contention, and undetected looping explorers.
Frame Relay End-to-End Keepalive
The Frame Relay End-to-End Keepalive feature enables the router to keep track of permanent virtual
circuit (PVC) status, independent of the switches in the Frame Relay network. The routers at both ends
of a PVC in a Frame Relay network engage in a keepalive session where one router issues keepalive
messages and the router at the other end of the PVC connection responds. The time interval for the
keepalive is configurable and is enabled on a per-PVC basis. As long as the keepalive-issuing router
receives response messages, the PVC status is up. When response messages are not received (because
of line failure, a faulty switch in the Frame Relay network, or a router failure), the PVC is down. This
mechanism enables bidirectional communication of PVC status to both routers at the ends of a PVC
connection.
Firewall Feature Set
The Cisco IOS Firewall feature set, available for a wide range of Cisco router platforms, adds greater
depth and flexibility to existing Cisco IOS software security capabilities, enriching features such as
authentication, encryption, and failover with robust firewall functionality and intrusion detection. A