Ethernet Switching
Ethernet Switching


‎05-11-2012 03:01 AM

Hi all


I need to understand how Juniper will perform if I have two different VLAN's running iSCSI and a single device that is a member of 1 of these VLAN's but needs to talk to both VLAN's i.e. through the routed interface. In the past I have seen when we create these types of interfaces (granted on Cisco), the router plane drops the packet size from 9126 to 1518 i.e. fragmentation happens. This fragmentation and re-assembly places a lot of stress on the devices and associated I/O
wait times because of the additional processing.

I need assurance that Juniper will not do this!!


If anyone can shed some light on this - PLS let me know

Ethernet Switching
Accepted by topic author Scotty_SA
‎08-26-2015 01:27 AM


‎05-11-2012 04:05 AM

Junos supports not fragmenting jumbo frams on routed interfaces from 11.2.


This is the kb with the configuration of the mtu on the Routed vlan interface


This it the description of the RVI in the documentation.


Routed VLAN Interface

In a traditional network, broadcast domains consist of either physical interfaces connected to a single switch or logical interfaces connected to one or more switches through VLAN configurations. Switches send traffic to hosts that are part of the same broadcast domain, but routers are needed to route traffic from one broadcast domain to another and to perform other Layer 3 functions such as traffic engineering. EX Series switches use a Layer 3 routed VLAN interface (RVI) named vlan to perform these routing functions, using it to route data to other Layer 3 interfaces. The RVI functions as a logical router, eliminating the need for having both a switch and a router.


The RVI (the vlan interface) must be configured as part of a broadcast domain or virtual private LAN service (VPLS) routing instance for Layer 3 traffic to be routed out of it. The RVI supports IPv4, IPv6, MPLS, and IS-IS traffic. At least one Layer 2 logical interface must be operational for the RVI to be operational. You must configure a broadcast domain or VPLS routing instance for the RVI just as you would configure a VLAN on the switch. Multicast data, broadcast data, or unicast data is switched between ports within the same RVI broadcast domain or VPLS routing instance. The RVI routes data that is destined for the switch’s media access control (MAC) address.


Jumbo frames of up to 9216 bytes are supported on an RVI. To route jumbo data packets on the RVI, you must configure the jumbo MTU size on the member physical interfaces of the RVI and not on the RVI itself (the vlan interface). However, for jumbo control packets—for example, to ping the RVI with a packet size of 6000 bytes or more—you must explicitly configure the jumbo MTU size on the interface named vlan (the RVI).

Steve Puluka BSEET - Juniper Ambassador
IP Architect - DQE Communications Pittsburgh, PA (Metro Ethernet & ISP)