Re: Switch Redundancy question !!
- From: "yellow" <fogqb@xxxxxxxxxxx>
- Date: 21 Jul 2006 23:43:47 -0700
yellow wrote:Thanks J
Thanks.Does it mean if I enable HSRP on both 3750 ports, it'll avoid L2 loop ?No.
All HSRP will do is protect against 3750 failure ( port / entire
switch) with respect to L3 default gateway for each of the VLANs
configured on the
Any other setting is required ?
Another question : I saw many posts about L2 & L3 redundancy, I'm
little confusing. I know STP is the solution for L2 redundancy & HSRP
/routing protocol is the soluton of L3.
If my L2 switch is capable of L3 switching, how do I configure the switch port to Layer 2 only, or to Layer 3.
to enable as layer 2: switchport
to enable as layer 3: no switchport
Sh int status will show port as routed when it is configured for use as
a layer 3 port
To avoid L2 loop on my setup, must I enable Layer3 on both 3750
inter-connect port ?
This gets more into the heart of basic LAN design. What function does
your 3750 switches serve now? Is "ip routing" enabled? Are your 3750s
acting in a L2-only capacity at present? Where are your L3 interfaces
in your VLANs?
I'm going to assume that your 3750s are acting as your core routers and
that your 2950s are distribution and access. I'm also assuming that
each 2950 contain one or more different VLANs. The L3 interfaces on
each VLAN are on each of the 3750s. Set up each link between the 2950s
and 3750s as 1Q trunks. If you want you can delve into VTP, vlan
pruning, allowed VLANs, native VLANs, etc but I won't cover that here.
Create your L3 interfaces on your 3750s. Set up HSRP on the L3 vlan
interfaces and point your users at that common IP for their gateway.
Don't forget to set HSRP preemption and priority (HSRP is really easy
to use). On your primary 3750 enable PVST and lower the priority on
your VLANS so that the primary 3750 becomes the root bridge.
spanning-tree vlan XYZ priority
You could also use the "root primary" options to set this for you.
That glosses over quite a bit of misc stuff but that's the gist of what
I think you're trying to do. It gives you a redundant L2 network
without making L2 or L3 changes to your hosts. Read up on HSRP. It's
really quite simple to use. I have example interface configs if
needed. One thing to point out is that HSRP doesn't turn itself on
until after you issue the "standby ip" command. The other standby
commands do nothing until that point. A good rule of thumb is
aaa.bbb.ccc.2 is your first HSRP member, .3 your second, .N etc and .1
is the actual standby IP.
You shouldn't have a L2 loop unless you pass the same VLANs between the
yes 3750 will be the core.
I want to active both 3750 (which means some wrkstation connects to
first 3750 & some are connecting to second 3750), and each 2950 dual
connect to both 3750, running multiple vlan, 1Q trunk is enable
between 2950 & the core. The core will handle vlan routing. If you
could post your example config of above requirement, it would be great.
For my scenario, I think routing (publicily known as L3 switching)
should be enable on 3750 port where connecting to 2950 , To enable
redundancy on the core switch, HSRP should be enable by interconnect
them using a utp cable, If I plug that cable between two core switches,
is it a L2 or L3 connection from switching point of view. If it's a L2
connection, it'll cause a L2 loop as each 2950 has dual path to the
root ? How do I configure the port to make it as a L3 connection ?
I know you may think my question is odd, I'm confusing with L2 & L3
redundancy. Some articles point out to avoid L2 loop in my scenario (I
thought my setup is a typical one, which has been used in many open
discussion, Access+Distribution layer dual connect to the Core layer),
it should enable L3 redundacy, I don't know how to configure it. Can
you help me ?
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