pert wrote: » There is no way to do this that I know of if you're uplinking to two 3750s. You could if youre uplinking to nexus switches, or a 6500 pair with VSS, but that's the only way I know how.
Eildor wrote: » What is the easiest (least switch configuration) way to achieve this on a 3750? I haven't read much about stacking, but it seems quite straight forward. What happens if the master goes down? The slave just takes over as the master right? How quickly does this happen? Also, I guess if you stacked the switches then you'd no longer need a FHRP for gateway redundancy -- or would you? I'm still not clear as to why I can't just configure the server in such a way that it shares traffic out of all links... is there a reason why this wouldn't work? As the access layer is routed, return traffic would be load balanced between the 2 switches anyway, so what's the big deal? I'm just curious as to why it wouldn't work.
srg wrote: » You're right about FHRP not beeing neede for redundancy, its all managed in the stack. With routed access this should be no problem, but you'll need double IP addresses on the server so might not be what you like. Go with the stack if you're able.
Eildor wrote: » This is for a University project, so I want to make use of a FHRP just to show I can. I'm still not entirely clear on how this is going to work... how will the 4 link EtherChannel to each switch work? Practically I guess what I need to do is configure the EtherChannels on the switches and servers, and then team the two NICs (two 4 port NICs) together? Am I going to have a problem with the gateways? Because what I'd need to do is use one gateway on one EtherChannel, and another gateway on the other EtherChannel (the access layer switches act as the gateway).
srg wrote: » If you have the two switches stacked, you make one 8 port etherchannel in the switchstack, and one 8 port team on the server. The server will think its connected to one switch, not two. You cannot do one team to two switches if they're not stacked (or vPC, or VSS). If the two switches are separate you can make a 4 port channel between each NIC and switch and use them as L2 Active/Passive. You might be able to route directly between the server and switch with a separate IP per team on the server and run it active/active but its really a hack.
Eildor wrote: » Can you tell me why this is technically not possible though; do you know? I just want to understand why I can't load balance between two EtherChannels connected to two different switches. I'm sure there is some reasonable technical explanation, but I just can't think of it. Thank you for your help.
networker050184 wrote: » The issue is the way MACs and IPs are bound and transmitted. So when you have a server with the IP address 10.0.0.1 and MAC address aaaa.aaaa.aaaa.aaaa the mac will be forwaded out a single interface on the switch. So what happens when that destination MAC starts being seen out of two destination in the network? Nothing good that's for sure. Forwarding tables contantly changing and traffic not getting to where it's supposed to. There are technologies that can make this function like pointed our with the Cisco Nexus.
Eildor wrote: » The access layer in this design is routed. I'm sorry, I should have mentioned that in the very first post. The ports connecting to servers are of course layer 2 ports, but the ports connecting to other switches (to distribution layer switches) are layer 3. There are no layer 2 connections between the two access layer switches. That makes it ok, right?
srg wrote: » Ok well that might work, but the server will have 2 IP adresses from different subnets and two separate gateways. So depending on the OS you might or might not get a good load balancing going.
networker050184 wrote: » What would be the benefit of this setup? What are you trying to accomplish? I know this is for a school project, but unnecessary complexity is never a good thing.
Eildor wrote: » 1. I want redundancy, which is why servers are dual-homed. 2. I also want to make use all links for extra bandwidth. 3. I want to use a FHRP protocol just to show I can. 4. I want something I can more or less implement on GNS3.
pert wrote: » I'm not an expert on all things theory but here's my explanation. 1 - You can't have Active/Active connections to two different switches due to spanning tree, to get around this you have to use a technology other than spanning tre 2 - Every technology that allows active/active that I know of requires the upstream switch to be one device logically, and have some sort of peer link/keepalive 3 - IIRC from NP studies, when a switch sees a MAC it already knows appear on a different port it updates the port the MAC is known on with the new port and the old entry/port no longer exists. I assume this is why the switches need to be one logical switch in order for it to be load balanced across two different pieces of hardware. This is why you need a switch stack, vPC, or VSS. My 2c
networker050184 wrote: » 1. Makes sense. 2. This is a bad design strategy. If you have enough traffic that you need to utilize your redundant links you are going to have a bad day when one of them actually breaks. This is a situation a lot of people find themselves in due to poor prior planning or exponetial growth. It's not something people usually willing design themselves into. 3. If I were your professor I'd want to see a well designed network. Not one that uses stuff just because. 4. Probably going to limit you from a lot of the fancy things you are trying to accomplish like the MLAG technologies you'd need.
srg wrote: » Let me turn this around; how did you think this would work? You have two switches with routing between them, server is connected to both switches and you're asking why it needs to have two different IP-addresses. How do you suppose it could manage with one IP address, connected to two different L3 domains?
networker050184 wrote: » It's going to come down to the OS and what type of traffic pattern you are running here. How is the upstream router going to route these packets? Most likely flow based so you end up worrying about hashing to try and get traffic to use more than one link. If you are using an FHRP and point the next hop as the VIP only one is going to respond anyway. Many things to consider here besides will packets technically flow.
Eildor wrote: » Why would it not work? I source traffic from a single IP address out of both interfaces, is that a big deal? Let's say I configured both access layer switches to use the same IP address on their SVIs, would that theoretically not work? I could even configure ports connecting to servers with the same MAC address if that helps with the NIC bonding process (I don't know about NIC bonding). Anyway, yes this is getting silly now ...I just found it to be an interesting problem to think about. But obviously there's already a solution which is much easier... just stack the bloody things! Thank you!
srg wrote: » This is gonna be all kinds of funky . Just stack them. If you're running L3 between the switches you're not gonna be able to run a FHRP anywho.
