How do you configure wide area network (WAN) protocols on the interface card for a Layer 3 (L3) switch? In this tip, experts Puneet Mehta and Dr. David Hughes go over L3 switching and explain how it reacts in WAN environments.
Layer 3 switching
From expert Puneet Mehta
Layer 3 (L3) switching refers to a class of high-performance routers optimized for the campus LAN or intranet, providing both wire-speed Ethernet routing and switching services.
An L3 switch router performs the following three major functions:
- Packet switching
- Route processing
- Intelligent network services
Compared to traditional routers that are microprocessor based, L3 switch routers are faster, as they use application-specific integrated circuit (ASIC) hardware. L3 multiprotocol switches (by default) come with the feature-rich operating system, which includes Layer 3 IP static routing, RIP, RIPv2, VRRP and OSPFv2 routing protocols. Depending on the product vendor, different levels of advanced feature upgrades might be available that will enable you to take advantage of a set of additional routing protocols such as IPX, AppleTalk, DVMRP, PIM-DM/SM, RSVP and other specialized protocols consisting of IPv6, BGP4 and OSI, along with load balancing and firewall features.
On the WAN side
Again, depending on the vendor, an optional Network Services Module (NSM) with a variety of Port Interface Cards (PICs) might be available that will provide WAN connectivity for E1, T1, PRI ISDN, BRI ISDN, asynchronous and synchronous communications, frame relay and X.25. Some of them even provide a L3 IP static routing, RIP, RIPv2, VRRP and OSPFv2 routing protocols. These routing features give the device ability to not only act as a managed Layer 3 switch, but also as a fully-specified router with WAN interfaces and capabilities.
Can an L3 switch be used in a WAN environment?
From WAN optimization expert David Hughes
The answer to this question is very situation and vendor specific. Typically an L3 switch has a smaller feature set than a WAN router. Before using an L3 switch for a WAN application you will need to check the following:
- Does your L3 switch have the physical interfaces you require, such as a T1 with integrated CSU/DSU?
- Does your L3 switch provide all the software features you require?
Some examples include frame relay and MPLS support, packet fragmentation and interleave for VoIP, header compression, firewall capabilities, etc. The features that matter most will depend on your individual situation. In general, most people prefer to buy a full featured WAN router as opposed to using an L3 switch so they don't have to worry about being caught without key features.
This was first published in May 2008