The ICMP Time Exceeded message notifies a host when a packet it sent has been discarded because it was “out of time.” Packets are not actually timed, but to prevent packets from being forwarded forever when there is a routing loop, each IP packet header includes a Time to Live (TTL) field. Routers decrement TTL by 1 every time they forward a packet; if a router happens to decrement TTL of a packet to 0, the router discards the packet and sends an ICMP Time Exceeded messag..
Multicast Listener Discovery Protocol
RFC 2710 defines specifications for the Multicast Listener Discovery (MLD) protocol. MLD is derived from IGMPv2 and is designed for IPv6. The operation of MLD is similar to IGMPv2. The major differences between IGMPv2 and MLD are as follows: ■ All the multicast devices on a subnet use a special IPv6 link-local address as their source address in their communication to other multicast devices. The use of the link-local source address prevents the MLD packet from traveling be..
Traffic-Shaping Adaptation on Frame Relay Networks
A shaper used with Frame Relay can be configured to vary the shaping rate over time based on the presence or absence of congestion. When there is no congestion, the shaper uses the shaping rate,but when congestion occurs, it lowers the shaping rate, eventually reaching a minimum shaping rate. The minimum rate can be configured, or default to 50 percent of the shaping rate. This lower rate is typically called either the minimum information rate (MIR) or the mincir. To lower t..
Security Information Monitoring System
This section covers how Cisco IDS can monitor and identify intruder-based attacks and how security information is monitored and acted upon. Cisco IDS uses multilayer protection options to prevent an attack from successfully reaching the end target system such as a file server or desktop computer. After the attack or intruder-based traffic is identified and determined to be intrusive, the network administrator can stop the attack before any serious damage occurs. This can inv..
Generic Traffic Shaping works on an entire interface to limit the rate that it sends data. This first version restricts all outbound traffic to 500,000 bits per second: Router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router(config)#interface FastEthernet0/0 Router(config-if)#traffic-shape rate 500000 Router(config-if)#exit Router(config)#end Router# You can also specify traffic shaping for packets that match a particular access-l..
