InterVlan Switching..

Unanswered Question
Dec 9th, 2009

Hi Everybody!

Normally network devices in different VLANs cannot communicate with one another without a router to route traffic between the VLANs. The question is: is it possible to ensure communication between VLANs at Layer 2?

Best regards,

Agata

I have this problem too.
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Jon Marshall Wed, 12/09/2009 - 01:47

agata.czekalska wrote:

Hi Everybody!

Normally network devices in different VLANs cannot communicate with one another without a router to route traffic between the VLANs. The question is: is it possible to ensure communication between VLANs at Layer 2?

Best regards,

Agata

Agata

To route between vlans you need either a router or L3 switch.

Without it there is no communication although there are private vlans where community/isolated vlans can take to the primary vlan.

Jon

vvasisth Wed, 12/09/2009 - 02:17

Unfortunatly if you are looking to route traffic b/w 2 vlans without a router or a layer 3 switch it wont be possible. However, you can use the consept known as bridging.

Bridging is necessary when non-routable protocols like Network Basic Input/Output System (NetBIOS) and Local-Area Transport (LAT) are used to communicate between devices that are connected across different segments. To make forwarding decisions, a device working as a bridge works at the data link layer (Layer 2) of the Open System Interconnection (OSI) model. If any network layer addressing is involved, the segments that are interconnected through the bridge should belong to the same network.

The following are different types of bridging techniques:

  • Transparent Bridging (TB) is used to bridge networks that use similar media. TB is mostly used in an Ethernet environment. A device configured for TB initially learns the location of the devices by looking at the source MAC addresses in the frames. Next it builds a bridging table containing the MAC addresses and the ports through which they are reachable. To forward or filter traffic on the ports, the destination address in the frames is compared with information in the bridging table. When multiple paths are available between any two segments to provide redundancy, the spanning tree algorithm is used. This prevents loops. Ethernet LAN switches are transparent bridges with enhanced functionality. The presence of such a bridge is transparent to the end devices that are connected through them.
  • Source-Route Bridging (SRB) is used by token ring networks to interconnect multiple token ring segments. SRB operates differently than TB by allowing the end devices to find the path toward the destination. This is accomplished by sending explorer frames. For SRB devices to make forwarding decisions, the path information is included in the Routing Information Field (RIF) in the frame header. The presence or absence of a RIF is indicated with the Routing Information Indicator (RII) using the first bit of the source address.
  • Source-Route Transparent Bridging (SRT) technique enables a device to simultaneously work as a TB and SRB. If a frame is received without any RIF, it is transparently bridged. If a RIF is available in a frame, it is bridged using SRB.
  • Source-Route Translational Bridging (SR/TLB) allows SRB and TB domains to be interconnected. SR/TLB is used for bridging between dissimilar media, such as Ethernet and token ring segments. The bridging device introduces and removes RIFs and other packet transformations necessary for connecting dissimilar media.
  • Remote or encapsulated bridging is a technique used for connecting LAN segments separated by a Wide-Area Network (WAN) using TB. LAN frames are encapsulated within and bridged across the WAN protocol. Remote Source-Route Bridging (RSRB) and Data-Link Switching Plus (DLSW+) are used for interconnecting SRB domains across a WAN. DLSw can also be used for interconnecting Ethernet and token ring segments.
  • A Cisco router can be configured for routing specific protocols and bridging other protocols at the same time. The Concurrent Routing and Bridging (CRB) feature allows a specific protocol to be routed on certain interfaces and bridged on other interfaces on the same device at the same time. However, CRB does not allow the routed and bridged domains to communicate. To overcome this limitation, use the Integrated Routing and Bridging (IRB) feature, which also provides the benefits of CRB.

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