Update to 2.5.0 broke DHCP relay
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I think i found the root cause.
DHCP-Server is Upstream (behind) WAN.
DHCP-Relay for example only on LAN.At least i found a hint in Syslog:
Feb 22 16:01:17 check_reload_status 363 Syncing firewall
Feb 22 16:01:18 php-fpm 326 /services_dhcp_relay.php: No suitable upstream interfaces found for running dhcrelay!I guess i know where the problem resides.
Our default configuration sets the dhcp-relay only for the interfaces, not for wan. Our DHCP-Servers resides are mostly upstream on the WAN side. We have some firewalls where that is different.
/etc/inc/services.inc
$srvifaces = array(); foreach ($srvips as $srcidx => $srvip) { $destif = guess_interface_from_ip($srvip); if (!empty($destif) && !is_pseudo_interface($destif)) { $srvifaces[] = $destif; } } /* Check for relays in the same subnet as clients so they can bind for * either direction (up or down) */ $srvrelayifs = array_intersect($dhcrelayifs, $srvifaces); /* The server interface(s) should not be in this list */ $dhcrelayifs = array_diff($dhcrelayifs, $srvifaces); /* Remove the dual-role interfaces from up and down lists */ $srvifaces = array_diff($srvifaces, $srvrelayifs); $dhcrelayifs = array_diff($dhcrelayifs, $srvrelayifs); /* fire up dhcrelay */ if (empty($dhcrelayifs) && empty($srvrelayifs)) { log_error(gettext("No suitable downstream interfaces found for running dhcrelay!")); return; /* XXX */ } if (empty($srvifaces) && empty($srvrelayifs)) { # Error is here log_error(gettext("No suitable upstream interfaces found for running dhcrelay!")); return; /* XXX */ }My dhcp-Server resides outside of any net within the firewall, therefore $servifaces
is empty, resulting in the error in syslog.My fix is to explicit add the upstream if there is none. I am not quite sure if this is the best variant. I would think that fixing guess_interface_from_ip() might be a better way.
if (empty($srvifaces)){ $srvifaces[] = "vmx0"; } if (empty($srvifaces) && empty($srvrelayifs)) { log_error(gettext("No suitable upstream interfaces found for running dhcrelay!")); return; /* XXX */ }If there is anything else you need to know please let me know.
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@victor_g
Further investigation on the upgraded 2.5.0 production environment shows (in/var/log/dhcpd.log)Feb 22 15:41:48 wight dhcrelay[82265]: Internet Systems Consortium DHCP Relay Agent 4.4.2 Feb 22 15:41:48 wight dhcrelay[82265]: Copyright 2004-2020 Internet Systems Consortium. Feb 22 15:41:48 wight dhcrelay[82265]: All rights reserved. Feb 22 15:41:48 wight dhcrelay[82265]: For info, please visit https://www.isc.org/software/dhcp/ **Feb 22 15:41:48 wight dhcrelay[82265]: Unsupported device type 24 for "lo0"** Feb 22 15:41:48 wight dhcrelay[82265]: Feb 22 15:41:48 wight dhcrelay[82265]: If you think you have received this message due to a bug rather Feb 22 15:41:48 wight dhcrelay[82265]: than a configuration issue please read the section on submitting Feb 22 15:41:48 wight dhcrelay[82265]: bugs on either our web page at www.isc.org or in the README file Feb 22 15:41:48 wight dhcrelay[82265]: before submitting a bug. These pages explain the proper Feb 22 15:41:48 wight dhcrelay[82265]: process and the information we find helpful for debugging. Feb 22 15:41:48 wight dhcrelay[82265]: Feb 22 15:41:48 wight dhcrelay[82265]: exiting.So perhaps the default upgrade is adding lo0 to the dhcrelay startup process?
The equivalent from the 2.4.5_1 environment is as follows:
Feb 22 15:47:00 wight dhcrelay: Internet Systems Consortium DHCP Relay Agent 4.4.1 Feb 22 15:47:00 wight dhcrelay: Copyright 2004-2018 Internet Systems Consortium. Feb 22 15:47:00 wight dhcrelay: All rights reserved. Feb 22 15:47:00 wight dhcrelay: For info, please visit https://www.isc.org/software/dhcp/ Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx4/00:0c:29:10:bf:e3 Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx4/00:0c:29:10:bf:e3 Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx7.888/00:0c:29:10:bf:15 Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx7.888/00:0c:29:10:bf:15 Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx6/00:0c:29:10:bf:ed Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx6/00:0c:29:10:bf:ed Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx5/00:0c:29:10:bf:0b Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx5/00:0c:29:10:bf:0b Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx3/00:0c:29:10:bf:01 Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx3/00:0c:29:10:bf:01 Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx2/00:0c:29:10:bf:d9 Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx2/00:0c:29:10:bf:d9 Feb 22 15:47:00 wight dhcrelay: Listening on BPF/vmx1/00:0c:29:10:bf:f7 Feb 22 15:47:00 wight dhcrelay: Sending on BPF/vmx1/00:0c:29:10:bf:f7 Feb 22 15:47:00 wight dhcrelay: Sending on Socket/fallback -
Ok i have to add, that this is a solution (WAN is always vmx0) for my case. The physical interface of another system has sure another name,
<interfaces>
<wan>
<enable></enable>
<if>vmx0</if>
Therefore more general it is s.th. like
$config[interfaces][wan][if]
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@fwcheck There's definitely something odd going on.
In the test scenario, I have a similar environment, with DHCP server on the dirty (WAN) side, using vmx0. This seems to be working correctly, as I get vmx0 in the$srvifaceslist.
But nolo0in any list.
Now adding more elements to the test environment to find the thing that triggers
lo0to get added to the list. -
@johnsdixon said in Update to 2.5.0 broke DHCP relay:
But no lo0 in any list.
Isn't that a good thing ?
lo0 is the local host or 127.0.0.1
dhcrelay can't operate on "lo0" :@johnsdixon said in Update to 2.5.0 broke DHCP relay:
Feb 22 15:41:48 wight dhcrelay[82265]: Unsupported device type 24 for "lo0"
which is rather logic.
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@gertjan But my production environment generates a startup command for the DHCP relay with
lo0included.
This is not there in 2.4.5_1, but following an upgrade to 2.5.0 this appears, and there is no functioning DHCP relay process started by default in that situation. What I'm trying to do is work out what is triggering the inclusion of thelo0within the startup process.
There is nolo0anywhere in my config, nor has disabling services (eg. squid, OpenVPN) on the production configuration gained me working DHCP forwarding. -
Redmine issue created:
https://redmine.pfsense.org/issues/11523 -
I tried the beta of 2.5, and discovered the same thing.
I posted my 2.5 findings in here:
[https://forum.netgate.com/topic/157022/not-sure-if-it-is-a-bug-or-not-dhcprelay-in-2-5?_=1614502774329](link url)Hope this helps.
I have upgraded to 2.5, and it seems to be working on my setup.Cheers
Elfranko
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@viktor_g
I can confirm, that this issue relates to routing as already mentioned on redmine, and it doesn't exist in earlier Versions of pfSense.Having this configuration, where LAN is for Management only, and WAN is for Connection to Internet Router, DHCP-Server is on opt2, and Test-Computer trying to get IP via DHCP is on opt3:
<interfaces> <wan> <enable></enable> <if>hn2</if> <blockbogons></blockbogons> <descr><![CDATA[WAN]]></descr> <spoofmac></spoofmac> <ipaddr>172.30.0.99</ipaddr> <subnet>16</subnet> <gateway>WANGW</gateway> </wan> <lan> <enable></enable> <if>hn0</if> <ipaddr>10.100.0.99</ipaddr> <subnet>16</subnet> <gateway></gateway> <gatewayv6></gatewayv6> <descr><![CDATA[LAN]]></descr> </lan> <opt2> <descr><![CDATA[TestDC]]></descr> <if>hn3</if> <enable></enable> <spoofmac></spoofmac> <ipaddr>10.199.0.1</ipaddr> <subnet>24</subnet> </opt2> <opt3> <descr><![CDATA[Test1]]></descr> <if>hn1</if> <enable></enable> <spoofmac></spoofmac> <ipaddr>10.99.1.1</ipaddr> <subnet>24</subnet> </opt3> </interfaces> <staticroutes> <route> <network>10.0.0.0/8</network> <gateway>Null4</gateway> <descr><![CDATA[Default bei RFC 1918, Private Class A]]></descr> </route> <route> <network>172.16.0.0/12</network> <gateway>Null4</gateway> <descr><![CDATA[Default bei RFC 1918, Private Class B]]></descr> </route> <route> <network>192.168.0.0/16</network> <gateway>Null4</gateway> <descr><![CDATA[Default bei RFC 1918, Private Class C]]></descr> </route> </staticroutes> <dhcrelay> <enable></enable> <interface>opt3</interface> <agentoption></agentoption> <server>10.199.0.11</server> </dhcrelay>The NULL-Routes are to avoid Packets with local Addresses going to Internet (implicit Routes of direct attached Subnets have higher Priority).
With this configuration you cannot start DHCP-Relay Service (dhcrelay).
If you modify the NULL-Route "10.0.0.0/8" to something where the Subnet to the DHCP-Server is not part of (in my configuration e.g. "10.0.0.0/9"), then everything works fine.
Remark: After modifying Routes you have to reboot pfSense, because already existing routes were not replaced, but the modified route is added (no automatic flush of routing cache).
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Try to apply Patch ID 7990de53bfc8267d1dd96636a175929a35cbe664 to fix DHCP Relay issue
see https://redmine.pfsense.org/issues/11475
@roland_v said in Update to 2.5.0 broke DHCP relay:
Remark: After modifying Routes you have to reboot pfSense, because already existing routes were not replaced, but the modified route is added (no automatic flush of routing cache).
Could you create a new redmine issue for this?
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@viktor_g
Because I'm not able to build pfSense from source, I tried last development snapshot built on Tue Mar 02 01:18:30 EST 2021.With this version the DHCP-Relay works as expected.
For "Error on updating routing table after modifying static routes" I will open a new redmin issue as requested.
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@viktor_g said in Update to 2.5.0 broke DHCP relay:
Try to apply Patch ID 7990de53bfc8267d1dd96636a175929a35cbe664 to fix DHCP Relay issue
Thanks, this patch fixed my identical problem.
For future reference, because some people might not know about it: See https://docs.netgate.com/pfsense/en/latest/development/system-patches.html for how to apply such patches to an existing installation.
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Christian -
Hi,
just stepped on the same issue with PfSense 2.6.0
The Patch didnt pass the check, so i can´t apply it.My setup contains several LAN adapters leading to several (/24) Subnets.
The DHCP server is reachable on a remote system via Open VPN.Can You help me out?
/usr/bin/patch --directory='/' -t --strip '2' -i '/var/patches/6241d97843a1b.patch' --check --forward --ignore-whitespace Hmm... Looks like a unified diff to me... The text leading up to this was: -------------------------- |From 7990de53bfc8267d1dd96636a175929a35cbe664 Mon Sep 17 00:00:00 2001 |From: Viktor G <viktor@netgate.com> |Date: Thu, 25 Feb 2021 16:42:35 +0300 |Subject: [PATCH] route_get() optimization. Fixes #11475 | |--- | src/etc/inc/interfaces.inc | 2 +- | src/etc/inc/util.inc | 50 +++++++++++++++++++++++++++++--------- | 2 files changed, 39 insertions(+), 13 deletions(-) | |diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc |index 35206915d92..307e76edcef 100644 |--- a/src/etc/inc/interfaces.inc |+++ b/src/etc/inc/interfaces.inc -------------------------- Patching file etc/inc/interfaces.inc using Plan A... Ignoring previously applied (or reversed) patch. Hunk #1 ignored at 6041. 1 out of 1 hunks ignored while patching etc/inc/interfaces.inc Hmm... The next patch looks like a unified diff to me... The text leading up to this was: -------------------------- |diff --git a/src/etc/inc/util.inc b/src/etc/inc/util.inc |index 6f94b0da41e..bc5178dee61 100644 |--- a/src/etc/inc/util.inc |+++ b/src/etc/inc/util.inc -------------------------- Patching file etc/inc/util.inc using Plan A... Ignoring previously applied (or reversed) patch. Hunk #1 ignored at 2692. Hunk #2 ignored at 2707. Hunk #3 ignored at 2755. 3 out of 3 hunks ignored while patching etc/inc/util.inc done /usr/bin/patch --directory='/' -f --strip '2' -i '/var/patches/6241d97843a1b.patch' --check --reverse --ignore-whitespace Hmm... Looks like a unified diff to me... The text leading up to this was: -------------------------- |From 7990de53bfc8267d1dd96636a175929a35cbe664 Mon Sep 17 00:00:00 2001 |From: Viktor G <viktor@netgate.com> |Date: Thu, 25 Feb 2021 16:42:35 +0300 |Subject: [PATCH] route_get() optimization. Fixes #11475 | |--- | src/etc/inc/interfaces.inc | 2 +- | src/etc/inc/util.inc | 50 +++++++++++++++++++++++++++++--------- | 2 files changed, 39 insertions(+), 13 deletions(-) | |diff --git a/src/etc/inc/interfaces.inc b/src/etc/inc/interfaces.inc |index 35206915d92..307e76edcef 100644 |--- a/src/etc/inc/interfaces.inc |+++ b/src/etc/inc/interfaces.inc -------------------------- Patching file etc/inc/interfaces.inc using Plan A... Hunk #1 succeeded at 6041 (offset -118 lines). Hmm... The next patch looks like a unified diff to me... The text leading up to this was: -------------------------- |diff --git a/src/etc/inc/util.inc b/src/etc/inc/util.inc |index 6f94b0da41e..bc5178dee61 100644 |--- a/src/etc/inc/util.inc |+++ b/src/etc/inc/util.inc -------------------------- Patching file etc/inc/util.inc using Plan A... Hunk #1 succeeded at 2692 (offset 43 lines). Hunk #2 failed at 2705. Hunk #3 succeeded at 2690 (offset 4 lines). 1 out of 3 hunks failed while patching etc/inc/util.inc done -
@wurst You can simply upgrade to the latest pfSense version
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@wurst. I am not quite sure i do understand your problem right:
Your DHCP-Server is outside of the nets of pfsense, upstream on the openVPN-Interface, right ?Does the dhcplog reveal anything ?
cat /var/log/dhcpd.log
If you login into the box and do a
#ps aux | grep "dhcrelay"
show that dhcrelay is running ?I am not quite sure if you can workaround using
/usr/local/sbin/dhcrelay [-id <for all interfaces which require DHCP>] -iu <your openvpn-interface> -a -m replace IP_dhcp-server1 IP_dhcpsever2
That might be a fast fix for the problem.
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@fwcheck
Hi, sorry for my late reply.
The system went productive, so I used the Switch for DHCP relaying.Now I am back with another System, next try.
Heres my test with the line You recommended:
/usr/local/sbin/dhcrelay -id em2 -iu ovpns2 -a -m replace 10.1.1.12 Requesting: em2 as upstream: N downstream: Y Requesting: ovpns2 as upstream: Y downstream: N Internet Systems Consortium DHCP Relay Agent 4.4.2-P1 Copyright 2004-2021 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Unsupported device type 23 for "ovpns2"--> Unsupported Device Type 23
OK. The openvpn adapter is not supported.
If I start it without specifying "-iu", the machine starts:/usr/local/sbin/dhcrelay -d -id em2 -a -m replace 10.1.1.12 Requesting: em2 as upstream: N downstream: Y Internet Systems Consortium DHCP Relay Agent 4.4.2-P1 Copyright 2004-2021 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on BPF/em2/00:0c:29:a0:6f:7c Sending on BPF/em2/00:0c:29:a0:6f:7c Sending on Socket/fallback Adding 8-byte relay agent option Forwarded BOOTREQUEST for 00:0c:29:38:09:f2 to 10.1.1.12 Adding 8-byte relay agent option Forwarded BOOTREQUEST for 00:0c:29:38:09:f2 to 10.1.1.12 Adding 8-byte relay agent option Forwarded BOOTREQUEST for 00:0c:29:38:09:f2 to 10.1.1.12The DHCP request ist recieved by DHCP Server 10.1.1.12, it replying with DHCP offer:
The Packet recieves at the Pfsense but nothing happens...
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I'm seeing the same issue as @wurst but on a new (currently testing) installation which has not previously seen DHCP relay operational and has not been put into production yet.
At our main site I have PFSense router #1 (2.6.0) running an OpenVPN server, on the LAN network of this router are Microsoft DHCP servers. (PFSense #1 LAN address, 10.0.1.254/16, DHCP server 10.0.0.200)
At the remote site PFSense (2.6.0) box #2 running an OpenVPN client in peer to peer mode with layer 3 tunnelling. (LAN address 10.20.1.254/16)
Routing is all set up and working well, and I have been doing all my initial testing simply using the local DHCP server on PFSense route #2. For various reasons (including DNS registration, and potential PXE boot to a WDS server) I would prefer to use DHCP relay back to the Microsoft DHCP servers rather than a local DHCP server.
So I disabled DHCP, enabled DHCP relay and it..... doesn't work. Here is a screenshot of the configuration:
Two VLAN's are configured (STUDENT and GUEST) but at the moment I am
only testing with the untagged VLAN, LAN.Tcpdump on PFSense #2 confirms DHCP discovers are being received from a test client on LAN, but nothing is being forwarded over the OpenVPN link. It wasn't until I was looking directly at /var/log/syslog that I noticed this error which lead me to this (and other) threads:
Nov 12 15:46:48 pfSense2 php-fpm[70836]: /services_dhcp_relay.php: No suitable upstream interfaces found for running dhcrelay!It appears that the dhcp relay daemon is not even being started at all. The "upstream interface" to the DHCP server would be the OpenVPN tunnel - which is already up and running at the time that I'm trying to start the DHCP relay.
Also, I do have interfaces "assigned" to the OpenVPN tunnel, as I know you can run an OpenVPN tunnel without doing this but this can have some limitations.
DHCP relay not working is unfortunate and is a bit of a showstopper for me to roll out this OpenVPN tunnel after doing 90% of the work setting it up and testing it. I also don't have a layer 3 switch at the remote site to do DHCP relay, as the site is very small with only 3 computers and 2 wireless base stations so doesn't warrant an expensive switch..
At the moment we have other equipment providing this VPN site-site link which has significant limitations and needs replacing - PFSense would do a much better job of it - if the DHCP relay would work for me...
I'm happy to provide logs and do testing on this issue, and while I'm somewhat of a FreeBSD noob I do have a lot of Linux experience so I can find my way around the command line fairly well.
At the moment the link is not in production, in fact PFSense router #2 which will be at the remote office is actually in my house at the moment, so I can test anything without disrupting anyone, so I have an ideal test environment.
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I've been playing around with running dhcrelay manually and noticed a couple of things.
One is that the OpenVPN tunnel is not allowed as an upstream interface:
/usr/local/sbin/dhcrelay -a -iu ovpnc1 -i em1 10.0.0.200 Requesting: ovpnc1 as upstream: Y downstream: N Requesting: em1 as upstream: Y downstream: Y Internet Systems Consortium DHCP Relay Agent 4.4.2-P1 Copyright 2004-2021 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on BPF/em1/00:1e:67:23:e4:d1 Sending on BPF/em1/00:1e:67:23:e4:d1 Unsupported device type 23 for "ovpnc1" If you think you have received this message due to a bug rather than a configuration issue please read the section on submitting bugs on either our web page at www.isc.org or in the README file before submitting a bug. These pages explain the proper process and the information we find helpful for debugging. exiting.However it seems that the -iu option is actually optional. So trying to run without this option is a lot more successful:
/usr/local/sbin/dhcrelay -a -i em1 10.0.0.200 Requesting: em1 as upstream: Y downstream: Y Internet Systems Consortium DHCP Relay Agent 4.4.2-P1 Copyright 2004-2021 Internet Systems Consortium. All rights reserved. For info, please visit https://www.isc.org/software/dhcp/ Listening on BPF/em1/00:1e:67:23:e4:d1 Sending on BPF/em1/00:1e:67:23:e4:d1 Sending on Socket/fallbackMonitoring with tcpdump I am much closer now:
tcpdump -n -i ovpnc1 port 67 or 68 -v tcpdump: listening on ovpnc1, link-type NULL (BSD loopback), capture size 262144 bytes 21:20:27.963577 IP (tos 0x0, ttl 64, id 60806, offset 0, flags [none], proto UDP (17), length 328) 172.23.0.2.67 > 10.0.0.200.67: BOOTP/DHCP, Request from e8:03:9a:e8:2f:b2, length 300, hops 1, xid 0x88500a27, secs 3328, Flags [Broadcast] Gateway-IP 10.20.1.254 Client-Ethernet-Address e8:03:9a:e8:2f:b2 Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: Discover Client-ID Option 61, length 7: ether e8:03:9a:e8:2f:b2 Hostname Option 12, length 9: "IT-LAPTOP" Vendor-Class Option 60, length 8: "MSFT 5.0" Parameter-Request Option 55, length 14: Subnet-Mask, Default-Gateway, Domain-Name-Server, Domain-Name Router-Discovery, Static-Route, Vendor-Option, Netbios-Name-Server Netbios-Node, Netbios-Scope, Option 119, Classless-Static-Route Classless-Static-Route-Microsoft, Option 252 Agent-Information Option 82, length 5: Circuit-ID SubOption 1, length 3: em1 21:20:27.982545 IP (tos 0x0, ttl 126, id 17644, offset 0, flags [none], proto UDP (17), length 353) 10.0.0.200.67 > 10.20.1.254.67: BOOTP/DHCP, Reply, length 325, xid 0x88500a27, Flags [Broadcast] Your-IP 10.20.130.1 Server-IP 10.0.0.200 Gateway-IP 10.20.1.254 Client-Ethernet-Address e8:03:9a:e8:2f:b2 Vendor-rfc1048 Extensions Magic Cookie 0x63825363 DHCP-Message Option 53, length 1: Offer Subnet-Mask Option 1, length 4: 255.255.0.0 RN Option 58, length 4: 86400 RB Option 59, length 4: 151200 Lease-Time Option 51, length 4: 172800 Server-ID Option 54, length 4: 10.0.0.200 Default-Gateway Option 3, length 4: 10.20.1.254 Domain-Name-Server Option 6, length 8: 10.0.0.253,10.0.0.249 Domain-Name Option 15, length 17: "dummy-domain.local^@" Netbios-Name-Server Option 44, length 4: 10.0.0.253 Netbios-Node Option 46, length 1: h-node Agent-Information Option 82, length 5: Circuit-ID SubOption 1, length 3: em1The request is being forwarded to the DHCP server at the other end of the openvpn link and the reply is coming back.
The request is being sent using the link local address of the OpenVPN link - 172.23.0.2, with Gateway-IP of 10.20.1.254 emended in the request - which is the router's IP address on the subnet which the DHCP query is being made from.
Unfortunately the Microsoft DHCP server is addressing its reply to 10.20.1.254, which is the Gateway-IP within the initial request, not the actually address that the request came from.
As a result dhcrelay seems to be ignoring the response. Close but still so far...
The -U option looks like it should help, however unfortunately it also won't accept the openvpn link as a valid interface.
Even when explicitly trying to bind dhcrelay to the LAN interface for upstream requests, it still uses the openvpn link local address as the source address.
I feel like some kind of firewall rewrite rule could help here as a workaround but I don't know enough about pf on bsd to know where to start.
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Ok, for anyone else coming across this thread in future, I've got it working thanks to this post.
In short, TUN devices don't have MAC addresses (which dhcrelay needs to bind to) but TAP devices do. So I followed the advice to switch both ends of the site-to-site link from TUN (layer 3) to TAP (layer 2) devices, and added the extra route options that are not set automatically for a TAP device to restore routing.
In my case at the server end I added
route-gateway 172.23.0.2and at the client endroute-gateway 172.23.0.1, so that both ends have routes pointing at each other. I didn't need to change any of my other static routes or firewall rules.After that I was able to enable DHCP relay through the GUI and it works. I even managed to do a successful PXE boot across the tunnel simply by adding the Windows Deployment server as an additional (3rd) DHCP server in DHCP relay settings.
The only issue I have now is that I really need to be able to forward one VLAN's DHCP requests to a different pair of DHCP servers on a different Windows domain than the other VLAN's, however only one forwarder can be enabled through the GUI.
Since it binds explicitly to certain interfaces it looks like I may be able to manually run a second copy of dhcrelay from something like the shellcmd package. Will give that a try tomorrow.
The only other option would be to add another DHCP relay upstream which is capable of redirecting requests to different DHCP servers based on a ruleset, but I'd like to avoid that if possible as it is just adding further complication.
