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Multi-vendor troubleshooting lab 8 of 12

DHCP relay and options across vendors

One Cisco DHCP server now serves three sites through Arista, MikroTik and FortiGate relays, and each site fails differently: a reply that can't get home, a relay that stamps the wrong address, and a firewall that still answers for itself. Fix all three and check the options that clients receive.

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It needs Lite: its 5 nodes are set to 5 vCPU and 5,376 MB in total. That fits the free demo too.

In your workspace: Shared, then Multi-vendor interoperability and troubleshooting guided labs, then 08 - DHCP relay and options across vendors

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Level
Intermediate
Time
About 65 minutes
Nodes need
5 vCPU, 5,376 MB
Smallest plan
Lite

The scenario

Larkfield is moving every site onto one central DHCP server, a Cisco router, R1. The three sites each have a different gateway vendor, and H1 stands in for a PC at each one, with one network card per site. Today none of the three sites gets the right lease.

DeviceInterfaceAddressRole
R1Gi0/010.50.0.1/24DHCP server
EOS1Ethernet1 / Ethernet210.50.0.11/24 / 10.61.0.1/24Relay for site A
CHR1ether1 / ether210.50.0.12/24 / 10.62.0.1/24Relay for site B
FGT1port1 / port210.50.0.13/24 / 10.63.0.1/24Relay for site C
H1eth0 / eth1 / eth2DHCPA PC at site A, B and C

Every lease should carry: an address from .21 upwards in the site's subnet (R1 excludes .1 to .20), the site's gateway, DNS server 10.50.0.53, the domain site-x.larkfield.example and option 150, the TFTP server 10.50.0.69 for desk phones.

What you’ll practise

  • Explain giaddr, and how a DHCP server uses it to choose a pool and reach the relay
  • Configure and read DHCP relay on EOS, RouterOS and FortiOS
  • Find a return-route fault from the server's own view
  • Find a relay that sets the wrong giaddr
  • Find a rogue local DHCP server on a firewall
  • Check the options a client really receives, including vendor options such as option 150

The tasks

  1. Prepare H1
  2. Test all three sites
  3. Site A, the reply that can't get home
  4. Site B, the wrong giaddr
  5. Site C, the firewall that answers first
  6. Check the options

The Lab Tasks pane has the scenario, these tasks, the checks to run, hints and the full solution.

Topology and devices

The network as it opens in EVE-NG, drawn from the lab’s own canvas, and the image each node runs.

Topology of DHCP relay and options across vendors5 nodes and 1 network, 7 links. Every link is listed as text below the diagram.R1EOS1CHR1FGT1H1Server-LANGi0/0ether1ether2eth1Ethernet1port1Ethernet2eth0port2eth2
5 nodes and 1 network, with the interface names each link uses. On a narrow screen, scroll the diagram sideways.
Every link, as text
  • R1 Gi0/0 to Server-LAN (network)
  • EOS1 Ethernet1 to Server-LAN (network)
  • CHR1 ether1 to Server-LAN (network)
  • FGT1 port1 to Server-LAN (network)
  • EOS1 Ethernet2 to H1 eth0
  • CHR1 ether2 to H1 eth1
  • FGT1 port2 to H1 eth2
Nodes in DHCP relay and options across vendors, with the image each runs and the vCPU and RAM it’s set to
NodeDeviceImage in Add NodeSet to
R1Cisco IOSvvios-adventerprisek9-m.spa.159-3.m91 vCPU, 512 MB
EOS1Arista vEOSveos-4.33.1.1F1 vCPU, 2,048 MB
CHR1MikroTik RouterOSmikrotik-7.14.21 vCPU, 256 MB
FGT1Fortinet FortiGatefortinet-FGT-v7.0.17.M-build06821 vCPU, 2,048 MB
H1Alpine Linuxclbalpinebase-alpine-base-3-20-31 vCPU, 512 MB

How to open this lab

  1. Sign in to your workspace at lab.cloudlabbox.com.

  2. In File Manager, open Shared, then the folder Multi-vendor interoperability and troubleshooting guided labs.

  3. Open 08 - DHCP relay and options across vendors and start its nodes, then open Lab Tasks for the scenario and the steps.

The lab is read-only. You can start the nodes and configure the devices, but changes to the topology can’t be saved. To change it, rebuild it in your own folder.

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CloudLabBox is independent of Arista Networks, Cisco, CompTIA, Fortinet, HPE, Juniper Networks and MikroTik. The lab follows exam topics and isn’t vendor training material; vendor names identify the exams and the images in the workspace.