RIP, EIGRP, OSPF, IS-IS, BGP, MPLS, VTP, STP.
frupert
New Member
Posts:
40
Joined:
Sun Aug 03, 2008 9:35 am
Certs:
CCNP

LACP vs PAgP

Tue Feb 22, 2011 5:13 pm

Hi Guys,

I have used Cisco switching for a few years, never been much good at switching, mostly routing. Last year I did some work for a company that sold HP switching though and we did a huge amount of etherchannels using LACP whether it be switch to switch or switch to host. Now I'm back somewhere with decent equipment and we are looking to setup 2 x Gigabit Trunks in a EtherChannel Group to provide added redundancy and additional speeds. A lot of the material in my books discusses PAgP but not LACP and even online not many Cisco channel group articles recommend LACP. I always thought LACP was the better protocol and provided greater interoperability? I also read on one guide that with Cisco Catalyst, LACP only provides the additional speeds, and if one physical link goes down the whole channel goes down. I have not read this elsewhere - is it correct?

Any thoughts? Advice?

Cheers!

Mark

zerojunkie
Senior Member
Posts:
369
Joined:
Mon Jan 26, 2009 5:59 pm

Re: LACP vs PAgP

Tue Feb 22, 2011 6:41 pm

frupert wrote:I also read on one guide that with Cisco Catalyst, LACP only provides the additional speeds, and if one physical link goes down the whole channel goes down. I have not read this elsewhere - is it correct?



Not that I know of. Unless maybe you've set min-links to same amount of links in your group.


Ether way, imo, it is the superior protocol.

javentre
Post Whore
Posts:
1971
Joined:
Fri Jul 09, 2010 7:38 pm

Re: LACP vs PAgP

Tue Feb 22, 2011 6:59 pm

LACP supports standby/backup ports for a bundle, this is nice if you're concerned with the uneven hash/load issue that can occur with odd numbers of links in a bundle. This is a big issue for some when working hardware with only 8 hash result buckets.
http://networking.ventrefamily.com

User avatar
swagger
Post Whore
Posts:
1395
Joined:
Mon Nov 23, 2009 7:55 pm
Certs:
CCNP, CCNA Sec

Re: LACP vs PAgP

Tue Feb 22, 2011 7:26 pm

Also, LACP is open standard vs PAgP which is Cisco Proprietary and can only be used between Cisco devices.

User avatar
burnyd
Post Whore
Posts:
3154
Joined:
Fri Nov 13, 2009 5:15 pm
Certs:
CCIE R&S/SP,CCNP-SP,JNCIA,VCP510,VCA-DCV

Re: LACP vs PAgP

Tue Feb 22, 2011 8:02 pm

swagger wrote:Also, LACP is open standard vs PAgP which is Cisco Proprietary and can only be used between Cisco devices.


realistically thats the majority of the difference.

We use Lacp for lots of things here. portchannel to esx hosts, switchs etc etc. Works great.
http://danielhertzberg.wordpress.com - I blog about networks!

User avatar
Vito_Corleone
Moderator
Posts:
9850
Joined:
Mon Apr 07, 2008 10:38 am
Certs:
CCNP RS, CCNP DC, CCDP, CCIP

Re: LACP vs PAgP

Tue Feb 22, 2011 8:10 pm

I need to get in the habit of using LACP. I've been using "on" exclusively and it's bitten me a couple times.
http://blog.alwaysthenetwork.com

just2cool
Member
Posts:
137
Joined:
Fri Dec 24, 2010 12:11 am
Certs:
Expired 350-001

Re: LACP vs PAgP

Tue Feb 22, 2011 8:32 pm

You know, I'm pretty sure xphil3 still doesn't believe me that LACP provides checks to make sure each link in the bundle is still up and functional over just using "on".

You should stir up his feathers again.

User avatar
Vito_Corleone
Moderator
Posts:
9850
Joined:
Mon Apr 07, 2008 10:38 am
Certs:
CCNP RS, CCNP DC, CCDP, CCIP

Re: LACP vs PAgP

Tue Feb 22, 2011 8:49 pm

I IMed him. It'll be interesting to see.

Channeling unconditionally can cause a loop if the other side isn't configured. This has happened to me twice in the past. I configure my side, and the tard on the other side configures his incorrectly, or incompletely. Hello looptown.
http://blog.alwaysthenetwork.com

javentre
Post Whore
Posts:
1971
Joined:
Fri Jul 09, 2010 7:38 pm

Re: LACP vs PAgP

Tue Feb 22, 2011 8:55 pm

I've seen it with an ON channel spread across 2 Sups ... one sup ended up in ROMMON, and the loop crushed a lot of stuff.
http://networking.ventrefamily.com

User avatar
sacox31s
Junior Member
Posts:
64
Joined:
Mon May 24, 2010 2:04 pm
Certs:
CCNP, ITILv3

Re: LACP vs PAgP

Tue Feb 22, 2011 9:48 pm

I always prefer the open standard if it does what I need it to do.

Even if the environment is homogeneous Cisco.

User avatar
mellowd
CCIE #38070
Posts:
13814
Joined:
Wed Jun 18, 2008 7:49 am
Certs:
CCIE (RS,SP), JNCIE-SP, BC-/SPNE/NP

Re: LACP vs PAgP

Wed Feb 23, 2011 3:14 am

Vito_Corleone wrote:I need to get in the habit of using LACP. I've been using "on" exclusively and it's bitten me a couple times.



How so? I always use 'on' and I've never been bitten. I'm interested to know if I've missed some gotchas

User avatar
DanC
Ultimate Member
Posts:
849
Joined:
Mon Oct 06, 2008 8:01 am
Certs:
CCNA, CCNA-W, CCNP

Re: LACP vs PAgP

Wed Feb 23, 2011 7:25 am

mellowd wrote:
Vito_Corleone wrote:I need to get in the habit of using LACP. I've been using "on" exclusively and it's bitten me a couple times.



How so? I always use 'on' and I've never been bitten. I'm interested to know if I've missed some gotchas


Yep me too, I think this has been discussed somewhere in another topic a while back, IIRC someone mentioned about accidentally creating loops, I'd like to understand how this could happen though?

javentre
Post Whore
Posts:
1971
Joined:
Fri Jul 09, 2010 7:38 pm

Re: LACP vs PAgP

Wed Feb 23, 2011 7:30 am

EtherChannels are a single logical link but multiple physical links, and both sides need to understand this.

A broadcast or multicast frame only goes down one link in a channel. If the receiving device gets one of these frames, but isn't aware certain ports are bundled, it will send the multicast or broadcast back up the channel on the other port. This can easily create loops. A similar issues can occur with unknown unicast flooding too.

I don't consider an "ON" EtherChannel a solution I'm willing to use on my network.
http://networking.ventrefamily.com

User avatar
mellowd
CCIE #38070
Posts:
13814
Joined:
Wed Jun 18, 2008 7:49 am
Certs:
CCIE (RS,SP), JNCIE-SP, BC-/SPNE/NP

Re: LACP vs PAgP

Wed Feb 23, 2011 7:43 am

But surely when you switch ports on 'ON' the device in question knows exactly what ports are bundled and you've configured all the required ports to be ON?

javentre
Post Whore
Posts:
1971
Joined:
Fri Jul 09, 2010 7:38 pm

Re: LACP vs PAgP

Wed Feb 23, 2011 7:47 am

mellowd wrote:But surely when you switch ports on 'ON' the device in question knows exactly what ports are bundled and you've configured all the required ports to be ON?
Server admins can unplug/replug cables and less than clueful staff aren't always careful when swapping out bad hardware (install and powering a device before putting in a config), etc.

That's just the user induced issues, it doesn't account for a misbehaving Sup stuck in ROMMON doing strange things (which I've experienced at 2 customer sites!).

Having both sides continually exchanging packets, to keep the bundle up, is cheap insurance. I like it when things in the network fail shut, not wide open. It's a similar argument for L2 links vs L3 links. L2 tends to fail wide open (packets flooding), L3 tends to fail shut (no neighbors = no routes).
http://networking.ventrefamily.com

User avatar
mellowd
CCIE #38070
Posts:
13814
Joined:
Wed Jun 18, 2008 7:49 am
Certs:
CCIE (RS,SP), JNCIE-SP, BC-/SPNE/NP

Re: LACP vs PAgP

Wed Feb 23, 2011 8:02 am

I must admit, in the the years I've set mine to 'ON' - I've never once experienced a loop, ever.

We don't have end users going to our datacenters, only our NOC and ourselves. We also don't run any sort of etherchannel or IGP directly with customer equipment.

I could see the remote possibility of a loop forming if people are plugging stuff in at will, but that just doesn't happen.


but maybe, just maybe...

javentre
Post Whore
Posts:
1971
Joined:
Fri Jul 09, 2010 7:38 pm

Re: LACP vs PAgP

Wed Feb 23, 2011 8:12 am

mellowd wrote:We don't have end users going to our datacenters, only our NOC and ourselves.
This is a very important distinction between our two environments.
http://networking.ventrefamily.com

User avatar
Vito_Corleone
Moderator
Posts:
9850
Joined:
Mon Apr 07, 2008 10:38 am
Certs:
CCNP RS, CCNP DC, CCDP, CCIP

Re: LACP vs PAgP

Wed Feb 23, 2011 8:24 am

I've had loops form twice due to misconfigured channels. At my last job we had another group's gear in our DC. I brought up a static channel, the other guy said he did as well. He either misconfigured it, or didn't bring it up at all. My side was treating both ports as a single, logical link. His side was treating them as individual links. The channel should have gone err-disable at some point, but it didn't. This may have been related to something in our config, I'm not sure.

The second time, the server tard was cabling some new Fujitsu blade centers and ran one cable to each DC core (like an MEC). I told him to fix it and not let them (yet another group) bring up his side until he did. He didn't. I should have used my head and shut the ports down until I had confirmation that he'd fixed the cabling. This took down a big chunk of our DC for a bit.

Dynamic channels would have avoided both of these issues.
http://blog.alwaysthenetwork.com

User avatar
mellowd
CCIE #38070
Posts:
13814
Joined:
Wed Jun 18, 2008 7:49 am
Certs:
CCIE (RS,SP), JNCIE-SP, BC-/SPNE/NP

Re: LACP vs PAgP

Wed Feb 23, 2011 8:36 am

I see. Makes sense

User avatar
ristau5741
Post Whore
Posts:
10451
Joined:
Tue Aug 21, 2007 2:15 pm
Certs:
Instanity

Re: LACP vs PAgP

Wed Feb 23, 2011 12:43 pm

on does not use LACP, nor PAgP, link aggregation is simply on.

check the background theory here
http://www.cisco.com/en/US/tech/tk389/t ... 4470.shtml

'
Next

Return to Cisco Routing and Switching

Who is online

Users browsing this forum: Otanx, that1guy15, xC0MMAND0x, zgil86 and 39 guests