How to configure and verify the DHCP relay for EX-series switches

SUMMARY:

This article provides information on how to configure and verify the DHCP relay for the EX-series switches.

SYMPTOMS:

How to configure and verify the DHCP relay for the EX-series switches.

CAUSE:

Configuring IRB Interfaces

Integrated routing and bridging (IRB) interfaces enable a switch to recognize which packets are being sent to local addresses so that they are bridged whenever possible and are routed only when needed. Whenever packets can be switched instead of routed, several layers of processing are eliminated. Switching also reduces the number of address look-ups.

Note: In versions of Junos OS that do not support Enhanced Layer 2 Software (ELS), this type of interface is called a routed VLAN interface (RVI).

To configure the routed VLAN interface:

1. Create the VLAN by assigning it a name and a VLAN ID:
   [edit]
user@switch# set vlans support vlan-id 111
2. Assign an interface to the VLAN by specifying the logical interface (with the unit statement) and specifying the VLAN name as the member:
   [edit]
user@switch# set interfaces ge-0/0/18 unit 0 family ethernet-switching vlan members support
3. Create the subnet for the VLAN’s broadcast domain:
   [edit]
user@switch# set interfaces irb unit 111 family inet address 10.0.0.0/8
4. Bind a Layer 3 interface with the VLAN:
   [edit]
user@switch# set vlans support l3-interface irb.111

   Note: If you are using a version of Junos OS that does not support ELS, you create a Layer 3 virtual interface named vlan

    

Recovering System Booted From Backup JUNOS Image

This article describes the issue of a system booting from the backup root partition after a file corruption occurs on the primary root partition. This article is targeted for SRX and EX devices at this time.

1. Problem

EX switches and SRX firewalls running Junos Release 10.4R3, or later, have added resiliency based on the “resilient dual-root partition”, which if the switch detects a corruption on the primary root file system, it boots from the alternate root partition.

When this occurs, you are notified in two ways: Alarm and Warning Banner

1.1. Alarm

The following alarm message is generated:

user@switch> show chassis alarms
1 alarms currently active
Alarm time Class Description
2011-02-17 05:48:49 PST Minor Host 0 Boot from backup root

1.2. Warning

***********************************************************************
**                                                                   **
**  WARNING: THIS DEVICE HAS BOOTED FROM THE BACKUP JUNOS IMAGE      **
**                                                                   **
**  It is possible that the primary copy of JUNOS failed to boot up  **
**  properly, and so this device has booted from the backup copy.    **
**                                                                   **
**  Please re-install JUNOS to recover the primary copy in case      **
**  it has been corrupted.                                           **
**                                                                   **
***********************************************************************

2. Cause & Solution

It is likely that the file system became corrupted due to a sudden power loss, or ungraceful shutdown of the system.

Repairing the primary partition when it is corrupted:

• When the primary partition detects a corrupt, the device boots from the backup partition; which then becomes the active partition. Remember that after every successive reboot, the system will try to reboot from the current active partition.
• You can repair the primary partition, without any downtime. No reboot is required after running the following commands.  However the Alarm and Banner will be displayed.

_{Note: As long as both of the partitions are healthy, there is no issue with running the switch on either of them. You only have to ensure that both the partitions are healthy, so that fail over can be done transparently between the two partitions, in case of any file corruption.}