A multihomed transit AS has more than one connection to the outside world and can still be used for transit traffic by other ASs (see Figure 4-6). Transit traffic (relative to the multihomed AS) is any traffic that has an origin or destination that does not belong to the local AS. Figure 4-6. Multihomed Transit AS Using BGP Internally and Externally Although BGP-4 is an exterior gateway protocol, it can still be used inside an AS as a pipe to exchange BGP updates. BGP ..
Smurf Attacks, Directed Broadcasts, and RPF Checks
A smurf attack occurs when a host sends a large number of ICMP Echo Requests with some atypical IP addresses in the packet. The destination address is a subnet broadcast address, also known as a directed broadcast address. Routers forward these packets based on normal matching of the IP routing table, until the packet reaches a router connected to the destination subnet. This final router then forwards the packet onto the LAN as a LAN broadcast, sending a copy to every device..
In Figure 20-15, the group traffic that flows over the path from the RP (R3) to R5 to R4 is called a shared distribution tree. It is also called a root-path tree (RPT) because it is rooted at the RP. If the network has multiple sources for the same group, traffic from all the sources would first travel to the RP (as shown with the traffic from host S1 in Figure 20-14), and then travel down this shared RPT to all the receivers. Because all sources in the multicast group use a ..
Suppose that a switch port is receiving BPDUs and the switch port is in the Blocking state. The port makes up a redundant path; it is blocking because it is neither a root port nor a designated port. It will remain in the Blocking state as long as a steady flow of BPDUs is received. If BPDUs are being sent over a link but the flow of BPDUs stops for some reason, the lastknown BPDU is kept until the Max Age timer expires. Then that BPDU is flushed, and the switch thinks..
IPv6 Route Filtering and Metric Manipulation in OSPF
OSPF Version 3 has many of the same features for route filtering and metric manipulation. There are two commands for configuring link costs. The first command changes the costs globally for all links according to their bandwidth values: Router1#configure terminal Enter configuration commands, one per line. End with CNTL/Z. Router1(config)#ipv6 router ospf 1 Router1(config-rtr)#auto-cost reference-bandwidth 1000 %OSPFv3: Reference bandwidth is change. ..
