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Switching loops can cause misleading entries in a switch's media access control (MAC) database and can cause endless unicast frames to be broadcast throughout the network. A loop can make a switch receive the same broadcast frames on two different ports, and alternatingly associate the sending MAC address with the one or the other port.
A switch virtual interface (SVI) represents a logical layer-3 interface on a switch. VLANs divide broadcast domains in a LAN environment. Whenever hosts in one VLAN need to communicate with hosts in another VLAN, the traffic must be routed between them. This is known as inter-VLAN routing.
Any IP datagram with a source or destination address set to a loopback address must not appear outside of a computing system, or be routed by any routing device. Packets received on an interface with a loopback destination address must be dropped. Such packets are sometimes referred to as Martian packets. [1]
NOTE: a RID is the highest logical (loopback) IP address configured on a router, if no logical/loopback IP address is set then the router uses the highest IP address configured on its active interfaces (e.g. 192.168.0.1 would be higher than 10.1.1.2). Usually the router with the second-highest priority number becomes the BDR.
When an interface has an address configured in a subnet, such as 192.0.2.1 in the 192.0.2.0/24 (i.e., subnet mask 255.255.255.0) subnet, and that interface is considered "up" by the router, the router thus has a directly connected route to 192.0.2.0/24. If a routing protocol offered another router's route to that same subnet, the routing table ...
Physically segmenting the broadcast domains using routers at Layer 3 (or logically with VLANs at Layer 2) in the same fashion switches decrease the size of collision domains at Layer 2. Routers and firewalls can be configured to detect and prevent maliciously inducted broadcast storms (e.g. due to a magnification attack).
A special case of private link-local addresses is the loopback interface. These addresses are private and link-local by definition since packets never leave the host device. IPv4 reserves the entire class A address block 127.0.0.0 / 8 for use as private loopback addresses. IPv6 reserves the single address ::1.
Another method to monitor networks is to use port mirroring (called "SPAN", for Switched Port Analyzer, by vendors such as Cisco, [1] and given other names, such MLXe telemetry by Brocade Communications and other vendors)(also known as MIRROR port) or a monitoring protocol such as TZSP on routers and switches. This is a low-cost alternative to ...