The weight, more fully titled administrative weight, allows a single router to examine inbound BGP Updates and decide which routes to prefer. The weight is not a BGP PA, but simply a Ciscoproprietary setting on a local router. In fact, it cannot be included in a BGP Update sent to another router, because there is no place in the Update message to include the weight. Table 13-10 summarizes the key points regarding BGP weight. Table 13-10 Key Features of Administrative Weight ..
TCP SYN Flood, the Established Bit, and TCP Intercept
A TCP SYN flood is an attack directed at servers by initiating large numbers of TCP connections, but not completing the connections. Essentially, the attacker initiates many TCP connections, each with only the TCP SYN flag set, as usual. The server then sends a reply (with TCP SYN and ACK flags set)—but then the attacker simply does not reply with the expected third message in the three-way TCP connection setup flow. The server consumes memory and resources while waiting ..
WFQ can be configured for a maximum of 4096 queues, called dynamic queues in WFQ show command output. Interestingly, the allowed configurable values are powers of 2, between 16 and 4096, inclusive. IOS restricts the values because WFQ performs a hash algorithm to classify traffic, and the hash algorithm only works when the number of queues is one of these valid values. Additionally, WFQ keeps eight hidden queues for overhead traffic generated by the router. WFQ uses a very l..
Access lists can manage or control traffic as it passes through a switch. When normal access lists are configured on a Catalyst switch, they filter traffic through the use of the Ternary content-addressable memory (TCAM). Recall from Chapter 2, “Switch Operation,” that access lists (also known as router access lists, or RACLs) are merged or compiled into the TCAM. Each ACL is applied to an interface according to the direction of traffic—inbound or outbound. Packets then..
Congestion Indication Support in FRF.8.1
For FRF.8.1, Cisco supports the bidirectional mapping of FECN and EFCI bits outlined in Table 8-5. Table 8-5. Table 8-5. EFCI and FECN Mapping for FRF.8.1 Frame Relay to ATM Direction Default The EFCI field in the ATM cell header is set to 1 if the FECN field in the Frame Relay headers is set. User configurable The EFCI field in the ATM cell header is set to a constant 0. ATM ..
