User guide
26 Release Notes for Cisco 2500 Series for Cisco IOS Release 12.0 T
New and Changed Information
OSPF Packet Pacing
The former OSPF implementation for sending update packets needed to be more efficient. Some
update packets were getting lost in cases where the link was slow, a neighbor could not receive the
updates fast enough, or the router was out of buffer space. For example, packets might be dropped
if either of these topologies existed:
• A fast router was connected to a slower router over a point-to-point link.
• During flooding, several neighbors dumped updates to a single router at the same time.
OSPF update packets are now automatically paced by a delay of 33 milliseconds. Pacing is also
added between retransmissions to increase efficiency and minimize lost retransmissions.
OSPF update and retransmission packets are sent more efficiently. Also, you can display the LSAs
waiting to be sent out an interface.
Time-Based Access Lists
It is now possible to implement access lists based on the time of day. To do so, you create a time
range that defines specific times of the day and week. The time range is identified by a name, and
then referenced by a function, so that those time restrictions are imposed on the function itself.
Currently, IP and IPX extended access lists are the only functions that can use time ranges. The time
range allows the network administrator to define when the permit or deny statements in the access
list are in effect. Prior to this feature, access list statements were always in effect once they were
applied. Both named or numbered access lists can reference a time range.
RIP Enhancements
Triggered extensions to IP RIP increase efficiency of RIP on point-to-point, serial interfaces.
Routers are used on connection-oriented networks to allow potential connectivity to many remote
destinations. Circuits on the WAN are established on demand and are relinquished when the traffic
subsides. Depending on the application, the connection between any two sites for user data could be
short and relatively infrequent.
There were two problems using RIP to connect to a WAN:
• Periodic broadcasting by RIP generally prevented WAN circuits form being closed.
• Even on fixed, point-to-point links, the overhead of periodic RIP transmissions could seriously
interrupt normal data transfer because of the quantity of information that hits the line every 30
seconds.
To overcome these limitations, triggered extensions to RIP cause RIP to send information on the
WAN only when there has been an update to the routing database. Periodic update packets are
suppressed over the interface on which this feature is enabled.
Cisco IOS Firewall Feature Set Platform Support
The Cisco IOS Firewall feature set is now available on 2600 and 3600 series products.
The Cisco IOS Firewall feature set extends the security technology currently available in Cisco IOS
software to provide firewall specific capabilities:
• Context-based Access Control (CBAC)
• Java blocking