NEXT_HOP Behavior on Multiaccess Media
A medium is considered multiaccess (MA) if routers connected to that medium can exchange data in a many-to-many relationship. Routers on an MA medium share the same IP subnet and can physically access all other routers on the medium in one hop (directly connected). Ethernet, FDDI, Token Ring, Frame Relay, and ATM are examples of multiaccess media. The rule that IP has on MA media is that a router should always advertise the actual originator of the route in case the route's s..
The following list describes the process that occurs when a radio card uses passive scanning: 1. The radio card automatically tunes to each RF channel, listens for a period of time, and records information it finds regarding access points on each channel. 2. 2. By default, each access point transmits a beacon frame every 100 milliseconds on a specific RF channel, which the administrator configures. 3. While tuned to a specific channel, t..
As a designer of secure networks, one of the first things you must consider is the vast interdependency of today's larger networks. The Internet is the best example, but within each organization there exists a microcosm of the Internet. From an attacker's perspective, these interdependencies allow for the attacker's goals to be met in any number of ways. As an example, assume an attacker wants to bring down your website. The following list outlines the attacker's options: ..
BGP, specifically BGP Version 4 (BGPv4), is the one routing protocol in popular use today that was designed as an Exterior Gateway Protocol (EGP) instead of as an Interior Gateway Protocol (IGP). As such, some of the goals of BGP differ from those of an IGP such as OSPF or EIGRP, but some of the goals remain the same. First, consider the similarities between BGP and various IGPs. BGP does need to advertise IPv4 prefixes, just like IGPs. BGP needs to advertise some informatio..
Configuring a PAgP EtherChannel
To configure switch ports for PAgP negotiation (the default), use the following commands: Switch(config)# interface type mod/num Switch(config-if)# channel-protocol pagp Switch(config-if)# channel-group number mode {on | {{auto | desirable} [non-silent]}} On all Cisco IOS–based Catalyst models, you can select between PAgP and LACP as a channel-negotiation protocol. Some older models, however, offer only PAgP, so the channel-protocol command is not available. Each inte..
