Differentiate L2 and L3 communication on Extreme 2

[Netomaniac]

Hi Guys,

I have seen people talking about L2 and L3 communication. But when it comes to extreme I have seen people mentioning about Extreme as a L2 bridge and gives it no respect for its L3 capability.

My question is if one side of the Extreme is connected to the Router were it will have to interface with the router at a L3 level and if on the other side it interfaces to L2 device, in the above scenario will the switch still be acting as a L2 bridge or as an L3 switch.

What differentiates L2 bridging and L3 Switching !!!

Neto....!!!!!!

"You are running fast to remain at the same place"

 

[rn4it]

I don't know if this will answer your quesiton or not, but here's a couple scenarios that we use.

At the Core we use Extreme's ESRP and OSPF for redundant connection from the edge to the core. Since we've been on the 7x Extremeware we've had no problems.

The second, scenario is we have a Summit48si running OSPF to a LAN extention providor to connect Head Office with Private connections to our Branch Offices. At Head Office we have 2 connections connecting us to the Service provider and then single connections to our branch offices. We use OSPF for automated failover from our primary E100 to our secondary E10 connections. We've had 1 problem in 3-5 years that was caused by the switch were we had to reboot the switch. All other problems were either with the telco or the service providor.

We will be use an Extreme switch in a new project that will automate the failover from our branch offices to Head Office to our DR site.

L2 Bridging - individual VLANs stay within themselves and don't communicate with other VLANs.

L3 Switching - indivual VLANs cross VLANs bby means of a router or routing mechinism. L3 switching is a switch with routing capabiliities, the router is virtualized so to speak.

hope this helps

 

[Netomaniac]

Thanks for the info,

Here I have a scenario were we have created VLAN's for routing the traffic on Extreme 48Si. But all these VLAN's use the IP address. IP address can be resolved only at Level 3 and VLAN's can be resolved at Level 2. I am getting confused here, since the switch needs to do both type of routing I really can't figure out what's going on.

On the North bound we connect use a router either CISCO or Juniper, I hope L3 switching takes place here until the packet is safely delivered to the port on the extreme and it does some kind of L2 bridging to make sure the ethernet packets are delivered to the L2 devices that are connected to the Extreme on the south side.

There are no L3 devices on the south side of the Siwtch. Does it make sense the way I explained could be the routing taking place in the Extreme Summit 48Si.

Please advice me....

Neto....!!!!!!

"You are running fast to remain at the same place

 

[ExtremeTek]

Example #1:
Crisco Router--V10/V20 Tagged--S48si--Untagged Host V10
VLAN 10 L3 IP |
VLAN 20 L3 IP *--Untagged Host V20

In the above scenario, the Extreme is acting as an L2 switch or bridge if you prefer. The Crisco router is providing L3 connectivity for hosts in the VLAN 10 subnet and VLAN 20 subnet. This is perfectly fine configuration and relatively simply, but not always the best solution for performance. Like most L3 switches, the Extreme will generally outperform a router because it provides L3 switching in hardware in its ASIC chipset. Routing in a switch is far less CPU intensive then in a traditional router. This is especially true for large quantities of packets of small size, e.g. IP Telephony.

Example #2
Crisco Router--V30 untagged--48si--Untagged Host V10
|
*--Untagged Host V20

In the above configuration there is a third VLAN between the S48si and the Crisco. Host to Host communications between V10 and V20 happen using IP Forwarding through the S48si with minimum delay and jitter. This also free's up the Crisco from having to process broadcast traffic on V10 and V20 and also frees up the Crisco's CPU from being taxed during V10 to V20 communications. The only time that Crisco gets involved is when V10 or V20 hosts leave the routing domain, e.g. go out the Internet, etc.

Notice the difference in the two configurations.

Example #1:
config vlan default delete ports 1-3
create vlan v10
config vlan v10 tag 10
create vlan v20
config vlan v20 tag 20
config v10 add ports 1 tagged
config v20 add ports 1 tagged
config port 1 display-string crisco
config v10 add ports 2 untag
config port 2 display-string v10host
config v20 add ports 3 untag
config port 3 display-string v20host

I have not defined any IP addresses on the S48si VLANs. In this case the Crisco handles all IP Forwarding. This may not always be the most desired configuration, but Cisco would probably like to say it is (whatever).

Example #2:
config vlan default delete ports 1-3
create vlan v10
config vlan v10 tag 10
config vlan v10 ipaddress 192.168.10.1/24
create vlan v20
config vlan v20 tag 20
config vlan v20 ipaddress 192.168.20.1/24
create vlan v30
config vlan v30 tag 30
config vlan v30 ipaddress 192.168.30.1/24
config v30 add ports 1 untag
config port 1 display-string crisco
config v10 add ports 2 untag
config port 2 display-string v10host
config v20 add ports 3 untag
config port 3 display-string v20host
enable ipforwarding
config iproute add default 192.168.30.2

I am assuming that the Crisco has IP address 192.168.30.2 on its V30 interface and that all routing is static. You get the general idea now through. Now the Extreme switch has IP addresses assigned to it's VLAN. It is configured to forward traffic between all VLANs that is has locally attached. Ths S48si will also send all non-local traffic to the Crisco for outbound route processing. This is a more common configuration nowadays versus Example #1. In the past everyone relied on the router. Today, more is being done in hardware by L3 switches. Example #1 is more like a traditional Router/Hub design. Example #2 takes advantage of L3 switching technology and is a more modern approach.

Either way works. Pick the best design that works for you.

Evil will always triumph, because good is dumb. - Darth Helmut, Space Balls

 

[rn4it]

Netomaniac

Do you have access to the switch? If so, the look at the config. If the VLAN's have IP's assigned to them and have IPfording enabled, then routing between the VLAN's will likely occur here at the S48si, being that it would be a direct connect. If IPforwarding on the switch is not enabled or there are no IP's assigned to the VLANs on the switch, then they would go to the default gateway to route to the other VLANs.

Also,
" IP address can be resolved only at Level 3 and VLAN's can be resolved at Level 2. I am getting confused here, since the switch needs to do both type of routing I really can't figure out what's going on." VLAN's aren't resolved at L2, they operate at L2. PC's/servers on separate VLAN's can't talk to one another unleass a router is allowing them to. In an L3 switch, the router is built into the switch, but needs to be enabled. In the Extreme would the use of enable ipforwarding command is used to allow traffic to route between the VLANs that have had IPforwding enabled on them and an IP address assigned to them.

hope this helps