Routed interface or SVI
Hi,
Been wondering for a while now but what's the difference of connecting a switch and a router together through an SVI or a L3 interface?
a) You assign a /30 to both sides in the same subnet
b) You create a /30 SVI and add a particular interface into that vlan where you will connect your router and assign the other ip to the router
You will probably get some unwanted broadcast in that domain, but apart from that what are the pros cons?
A
Been wondering for a while now but what's the difference of connecting a switch and a router together through an SVI or a L3 interface?
a) You assign a /30 to both sides in the same subnet
b) You create a /30 SVI and add a particular interface into that vlan where you will connect your router and assign the other ip to the router
You will probably get some unwanted broadcast in that domain, but apart from that what are the pros cons?
A
Comments
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vinbuck
Member Posts: 785 ■■■■□□□□□□
That's not entirely true....
Two uplinks from a switch to two different routers in the same VLAN will be in a forwarding state. There has to be a loop in the topology to block a link. The OP is talking about putting in a /30 and doesn't mention multiple links. This depends on your hardware and what flexibility you want to have. You can drop out multiple links in the same VLAN/Subnet if you use an SVI.
For a /30, it all comes down to design preference as both types of routed links will be handled by CEF in a similar fashion with similar performance on most Cisco multilayer switches.
Good article on this here
Convergence Delays: SVI vs Routed Interface - Packet LifeCisco was my first networking love, but my "other" router is a Mikrotik... -
ColbyG
Member Posts: 1,264
Routed links are usually cleaner, and leave slightly less room for mistakes down the road. I only use SVIs if I need multiple devices on routed links, say two routers and two switches, then I'll use an SVI and /29. -
Forsaken_GA
Member Posts: 4,024
Routed links are usually cleaner, and leave slightly less room for mistakes down the road. I only use SVIs if I need multiple devices on routed links, say two routers and two switches, then I'll use an SVI and /29.
This is the same way I run. An SVI for a point to point routed link is pointless, you're using a port for layer 3 access either way. If more than two devices are going to exist on the subnet, then I use an SVI. -
Forsaken_GA
Member Posts: 4,024
Actually, now that I'm thinking about this.... if your router is running a trunk link back to the switch, then you'd use an SVI as opposed to a routed port on the switch. I've seen this on a few occasions where the router was limited on ports, and a link was trunked because it needed to do double duty as a transit link and a management link, and the management traffic needed to be isolated.
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MrBishop
Member Posts: 229
The names point you in the direction of were you should implement them in the network. SVI's for running traffic over the trunk links connecting switches together and router ports running from the switch to the router. Just clicked with me and this thread cleared it up!Degrees
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Certificaions
Currently pursuing: CCIE R&Sv5 -
Akiii
Member Posts: 80 ■■□□□□□□□□
That's not entirely true....
Two uplinks from a switch to two different routers in the same VLAN will be in a forwarding state. There has to be a loop in the topology to block a link. The OP is talking about putting in a /30 and doesn't mention multiple links. This depends on your hardware and what flexibility you want to have. You can drop out multiple links in the same VLAN/Subnet if you use an SVI.
For a /30, it all comes down to design preference as both types of routed links will be handled by CEF in a similar fashion with similar performance on most Cisco multilayer switches.
Good article on this here
Convergence Delays: SVI vs Routed Interface - Packet Life
Great article Sir! -
cxzar20
Member Posts: 168
That's not entirely true....
Two uplinks from a switch to two different routers in the same VLAN will be in a forwarding state. There has to be a loop in the topology to block a link. The OP is talking about putting in a /30 and doesn't mention multiple links. This depends on your hardware and what flexibility you want to have. You can drop out multiple links in the same VLAN/Subnet if you use an SVI.
For a /30, it all comes down to design preference as both types of routed links will be handled by CEF in a similar fashion with similar performance on most Cisco multilayer switches.
Good article on this here
Convergence Delays: SVI vs Routed Interface - Packet Life
That is right, I was bringing up the point about SVI in addition to the issue raised by the OP. If you have multiple links from a device coming into another with an SVI then spanning tree considerations have to be made. An example of this would be multiple uplinks to a stacked switch SVI. Even though they may go to two separate physical switches it acts as one logical and thus one of those links will be blocked if it isn't root.
