Information Technology Reference
In-Depth Information
IEEE 802.1p
The IEEE 802.1p signaling technique is an OSI Layer-2 standard for prioritizing network traffic
at the data link/MAC sub-layer. It can be characterized as a best-effort service at Layer 2. IEEE
802.1p traffic is simply classified (using 3 priority bits) and sent to the destination; no special
bandwidth services are established for the prioritized frames.
IEEE 802.1p is a subset of the 802.1q virtual local-area network (VLAN) trunking standard.
The 802.1q standard specifies a tag that is appended to a MAC frame just after the MAC
address, or just after the Routing Information Field (RIF), if a RIF is present. The VLAN tag
carries VLAN information. The VLAN tag has two parts: VLAN ID (12 bits) and prioritization
(3 bits). The 802.1p implementation defines this prioritization field.
802.1p establishes eight levels (3 bits) of priority, which is similar to IP Precedence. Network
adapters and switches can route traffic based on the priority level. Using Layer-3 switches
allows you to map 802.1p prioritization to IP Precedence before forwarding to routers. Because
802.1p is defined at Layer 2, it supports network layer protocols, such as IPX, SNA, and
AppleTalk, in addition to IP.
Load Balancing
The Cisco blueprint lists load balancing as a performance management topic. Load balancing
support for each routing protocol is covered in Chapter 7, “Static Routing and Distance Vector
Routing Protocols,” Chapter 8, “IP Link-State Routing Protocols,” and Chapter 9, “Border
Gateway Protocol.” For easy reference, Table 11-2 lists the load balancing capabilities covered
on each routing protocol.
Load Balancing Support
Table 11-2
Protocol
Load Balancing Support
Enhanced Interior Gateway Protocol (EIGRP)
Unequal-cost load balancing up to six paths
Open Shortest Path First (OSPF)
Equal-cost load balancing up to six paths
Intermediate System-to-Intermediate System
(IS-IS)
Equal-cost load balancing up to six paths
(Interior Gateway Routing Protocol (IGRP)
Unequal-cost load balancing up to six paths
RIP version 1 (v1) and RIPv2
Equal-cost load balancing
Border Gateway Protocol (BGP)
By default, selects only one path, but supports load
balancing with BGP Multipath to the same
autonomous system (AS)
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