Layer 3 switch over the router

Tiras25
Tiras25 used Ask the Experts™
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I have a situation.  Moving users to the new office.  Cisco gear however 4 to 6 weeks delayed.  Looking for a temp solution.  
I have a Juniper EX4300 switch.   Can I configure it as layer 3 as a router to serve the purpose.  Would that be any difference than having a router?  It should have GBIC ports for ISP.   And enough mbit ports for the users.   There should be only 10-15 users initially.

Any other temp ideas guys?  Thanks.
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Distinguished Expert 2018

Commented:
Generally, most of the switches can't be used as WAN routers since NAT is not supported on switches. Juniper EX4300 does not support NAT. If you have  virtual private LAN L2/L3 service provided by ISP link between locations and NAT is performed on some other device than you can use EX as CE device (or if you are using public IP addresses on all your end devices).
Problem can also be any other protocol that is needed and not supported on EX device.
Layer 3 Protocols Not Supported on EX Series Switches
Rakesh Madupu JNCIE-SP #02079 CCIE-SP#47613Network Development Engineer

Commented:
There is absolutely no problem configuring the ports as layer-3. Delete family ethernet switching and configure them for family inet, on the other hand, if you wanted to only have ethernet switching, configure port as access and configure an vlan.x as an l3 interface, follow the below link and revert for any help.

https://www.juniper.net/documentation/en_US/junos/topics/reference/general/ex-series-l3-protocols-supported.html

-R

Commented:
I'd buy a Cisco 1841 off ebay for about £40.  Use that until the equipment comes.  A simple NAT config is dead easy.
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Author

Commented:
1841 model?
Does it have Gb fibre ports for SFP LC mmode?

Commented:
Sorry, no, I didn't take note of the gbic requirement
Distinguished Expert 2018

Commented:
There is no need for SFP on temporary router. You can use SFP on switch just to bring connection with ISP up.

[ISP router] --- fiber optic --- [Juniper SFP ge-0/1/3] -- vlanX-- [router WAN interface gi0/0 - Juniper ge-0/0/23] --- [router inside interface gi0/1- Juniper ge-0/0/22]

Explanation (Juniper 24 ports switch; Cisco 2 port router):

configure Juniper switch ports ge-0/1/3 and ge-0/0/23 to belong to the same VLAN
on SFP port ge-0/1/3 connect link with ISP
on RJ45 port ge-0/0/23 connect WAN router's interface (e.g fa0/0)
This will create point-to-point link between PE and CE routers (it will work except in the case that subnet mask is /31)

Router's inside interface (fa0/1) connect to port ge-0/0/22
Configuration of ports depends on your switch configuration and future plans. But, generally, can be configured as point to point link/VLAN (default route point to router as next hop) or as trunk (subinterfaces for each VLAN on router's side - trunk on Juniper). Point-to point is preferred.

Author

Commented:
I thought the switch cannot do NAT  and no IPSEC.  Need firewall for that.  I don't have it either yet.
Distinguished Expert 2018
Commented:
Switch cannot provide NAT and IPsec, it will just provide connection to ISP in this design (the same function as media converter). Comment was related how to use 1841 with Juniper switch without SFP on router (since it would be temporary router) - Juniper switch can provide SFP that is not present on router (why wast money :) ).
Router will need to be configured for NAT and IPsec, Cisco routers are also capable to be configured as Zone based firewalls.

Basically, this topology:
How to use router without SFP and switch to connect to ISP via SFP :)The rest of the ports on switch of course belong to internal network (or whatever you want)

Author

Commented:
Thank you!  I see you indicated a PE router.  In my case the ISP doesn't provide any routers.  I indicated I will provide my own router.
Distinguished Expert 2018
Commented:
ISP is providing router. Is PE router located on your or some distant location is irrelevant.
:)

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