dhclient in the installer does not support rfc3442-classless-static-routes

Solution Verified - Updated -

Environment

Red Hat Enterprise Linux 7
Version-Release number of selected component:
RHEL-7.3 installer (rhel-server-7.3-x86_64-dvd.iso)
RHEL-7.4 installer (rhel-server-7.4-x86_64-dvd.iso)
RHEL-7.5 installer (rhel-server-7.5-x86_64-dvd.iso)

Issue

Dracut DHCP is failing to recognize rfc3442-classless-static-routes option. It occurs only when DHCPbooting on network is offering only classless static routes.

Resolution

Use RHEL-7.6 (or newer) Installer.
Mentioned bug has been resolved in updated package dracut-033-554.el7.x86_64.rpm which is a part of the RHEL-7.6 images
More information could be found in the following bug advisory: RHBA-2018:3232

Root Cause

dhclient.conf in dracut has classless-routes instead of classless-static-routes:

current /etc/dhclient.conf file:

option classless-routes code 121 = array of unsigned integer 8;

request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, domain-search, host-name,
        root-path, interface-mtu, classless-routes;

but it should have classless-static-routes as per following example - /etc/dhclient.conf:

option classless-static-routes code 121 = array of unsigned integer 8;

request subnet-mask, broadcast-address, time-offset, routers,
        domain-name, domain-name-servers, domain-search, host-name,
        root-path, interface-mtu, classless-static-routes;

Diagnostic Steps

How to reproduce it:
The steps to reproduce the bug are to boot into the initramfs image included in the rhel-server-7.3-x86_64-dvd.iso in a DHCP environment with option rfc3442-classless-static-routes.

Actual results:
When the system boots, only the route to the local gateway is present (all rfc3442-classless-static-routes (DHCP option 121) are being ignored.

Expected results:
rfc3442-classless-static-routes (DHCP option 121) are available when the system boots.

This solution is part of Red Hat’s fast-track publication program, providing a huge library of solutions that Red Hat engineers have created while supporting our customers. To give you the knowledge you need the instant it becomes available, these articles may be presented in a raw and unedited form.

Comments