DHCP sending incorrect gateway in DHCP Reply
Sten Carlsen
stenc at s-carlsen.dk
Wed Oct 16 16:14:43 UTC 2019
First reaction:
You define the classes inside the subnets, this is dangerous as they inherit from that subnet and use that in other subnets.
--
Best regards
Sten Carlsen
For every problem, there is a solution that
is simple, elegant, and wrong.
HL Mencken
> On 16 Oct 2019, at 16.07, Eric Koons <ekoons5159 at gmail.com> wrote:
>
> I’m having an issue with ISC DHCP where it’s sending the incorrect router option/gateway in the DHCP reply. Any help is appreciated.
>
> Below is a capture using TCPDUMP on the DHCP server. With this particular request, it should be sending the Gateway of 10.123.4.41, but it’s sending 10.123.4.49 which is the gateway option defined in the other scope. It almost seems like the first device in a DHCP scope that comes online the Server uses that as the router option for all other requests. I’ve also attached a copy of the dhcpd.conf file below. This is on a CENTOS server: CentOS Linux release 7.7.1908 (Core).
>
> 09:57:27.101056 00:a5:bf:9d:a9:59 > 00:50:56:ae:be:10, ethertype IPv4 (0x0800), length 442: (tos 0xc0, ttl 29, id 53170, offset 0, flags [none], proto UDP (17), length 428)
> 10.123.4.41.bootps > 10.123.0.9.bootps: [udp sum ok] BOOTP/DHCP, Request from 00:18:48:02:6e:a0, length 400, xid 0xcc58406, Flags [none] (0x0000)
> Gateway-IP 10.123.4.41
> Client-Ethernet-Address 00:18:48:02:6e:a0
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message Option 53, length 1: Request
> Server-ID Option 54, length 4: 10.123.0.9
> Requested-IP Option 50, length 4: 10.123.4.45
> Parameter-Request Option 55, length 12:
> Subnet-Mask, BR, Time-Zone, Default-Gateway
> Domain-Name, Domain-Name-Server, Hostname, Vendor-Option
> Time-Server, BF, TFTP, WWW
> Vendor-Option Option 43, length 86: 2.3.82.80.68.3.9.69.67.77.58.101.83.65.70.69.4.7.57.49.48.52.50.48.53.5.5.48.46.48.46.49.6.7.49.95.53.48.95.50.51.7.5.48.46.48.46.49.8.6.48.48.49.56.52.56.9.6.53.50.48.48.48.49.10.20.86.101.99.105.109.97.32.78.101.116.119.111.114.107.115.32.73.110.99.46
> Vendor-Class Option 60, length 3: "RPD"
> Client-ID Option 61, length 15: hardware-type 255, 48:02:6e:a0:00:03:00:01:00:18:48:02:6e:a0
> Agent-Information Option 82, length 18:
> Circuit-ID SubOption 1, length 6: ^@^D^@^@^@^C
> Remote-ID SubOption 2, length 8: ^@^F^@M-^^^^]YM-^
> END Option 255, length 0
> 09:57:27.101623 00:50:56:ae:be:10 > 00:00:0c:07:ac:00, ethertype IPv4 (0x0800), length 381: (tos 0x0, ttl 64, id 62282, offset 0, flags [DF], proto UDP (17), length 367)
> 10.123.0.9.bootps > 10.123.4.41.bootps: [bad udp cksum 0x1a94 -> 0xcaaa!] BOOTP/DHCP, Reply, length 339, xid 0xcc58406, Flags [none] (0x0000)
> Your-IP 10.123.4.45
> Gateway-IP 10.123.4.41
> Client-Ethernet-Address 00:18:48:02:6e:a0
> Vendor-rfc1048 Extensions
> Magic Cookie 0x63825363
> DHCP-Message Option 53, length 1: ACK
> Server-ID Option 54, length 4: 10.123.0.9
> Lease-Time Option 51, length 4: 86400
> Subnet-Mask Option 1, length 4: 255.255.255.248
> BR Option 28, length 4: 10.123.4.55
> Time-Zone Option 2, length 4: -18000
> Default-Gateway Option 3, length 4: 10.123.4.49
> Domain-Name Option 15, length 13: "rpd.sectv.com <http://rpd.sectv.com/>"
> Domain-Name-Server Option 6, length 4: 10.123.0.9
> Vendor-Option Option 43, length 10: 61.8.10.123.4.10.10.123.4.58
> Time-Server Option 4, length 4: 10.123.0.9
> Agent-Information Option 82, length 18:
> Circuit-ID SubOption 1, length 6: ^@^D^@^@^@^C
> Remote-ID SubOption 2, length 8: ^@^F^@M-^^^^]YM-^
> END Option 255, length 0
>
> Here is a copy of my dhcpd.conf:
>
> #Global Options:
>
> #Set the server to authoritative;
> authoritative;
>
> option domain-name-servers 10.123.0.9;
> option log-servers 10.123.0.9;
> option ntp-servers 10.123.0.9;
> option time-servers 10.123.0.9;
>
> local-address 10.123.0.9;
>
> #Time Offset
> option time-offset -18000;
>
> #Lease time
> default-lease-time 86400;
> max-lease-time 172800;
>
>
>
> #Time zone
> option PCode code 100 = text;
> option TCode code 101 = text;
> option PCode "”EST5EDT4,M3.2.0/02:00,M11.1.0/02:00";
> option TCode "America/New_York”";
>
> #Remote Phy Stuff
> # option CCAPCore code 43 = string;
> # option iNode-manager code 43 = string;
>
> option space VCM;
> option VCM.ccap_cores code 61 = { array of ip-address };
>
> default-lease-time 86400;
> max-lease-time 172800;
>
>
> # Use this to enble / disable dynamic dns updates globally.
> # ddns-updates on;
> # ddns-update-style interim;
> # ddns-rev-domainname "in-addr.arpa";
> # deny declines;
> # deny bootp;
> #allow client-updates;
>
> # key dhcpupdate {
> # algorithm hmac-md5;
> # secret iY+hMAmhBJvhxc82gX8Vgg==;
> # }
>
> # zone sectv.com <http://sectv.com/>. {
> # primary 10.0.40.5;
> # key dhcpupdate;
> # }
>
> # zone 10.123.in-addr.arpa. {
> # primary 10.0.40.5;
> # key dhcpupdate;
> # }
>
>
> # Use this to send dhcp log messages to a different log file (you also
> # have to hack syslog.conf to complete the redirection).
> log-facility local7;
>
> #10.123.0.0/24 Subnet - Management
> subnet 10.123.0.0 netmask 255.255.255.0 {
> #No options or ranges defined - No DHCP
> }
>
> # 10.123.4.40/29 Subnet
> subnet 10.123.4.40 netmask 255.255.255.248 {
> range 10.123.4.42 10.123.4.46;
> option subnet-mask 255.255.255.248;
> option domain-search "sectv.com <http://sectv.com/>";
> option routers 10.123.4.41;
> option broadcast-address 10.123.4.47;
> # class "CiscoRPD" {
> # match if option vendor-class-identifier="RPD";
> vendor-option-space VCM;
> option VCM.ccap_cores 10.123.4.10, 10.123.4.58;
> option domain-name "rpd.sectv.com <http://rpd.sectv.com/>";
> # }
> # class "CiscoiNode"{
> # match if option vendor-class-identifier="Cisco.iNode.oib.1.0";
> # option iNode-manager 01:04:0a:7b:00:0a;
> # option tftp-server-name "10.123.0.9";
> # option bootfile-name "inode.bin";
> # option domain-name "inode.sectv.com <http://inode.sectv.com/>";
> # }
> }
>
> # 10.123.4.48/29 Subnet
> subnet 10.123.4.48 netmask 255.255.255.248 {
> range 10.123.4.50 10.123.4.54;
> option subnet-mask 255.255.255.248;
> option domain-search "sectv.com <http://sectv.com/>";
> option routers 10.123.4.49;
> option broadcast-address 10.123.4.55;
> class "CiscoRPD" {
> match if option vendor-class-identifier="RPD";
> vendor-option-space VCM;
> option VCM.ccap_cores 10.123.4.10, 10.123.4.58;
> option domain-name "rpd.sectv.com <http://rpd.sectv.com/>";
> }
> # class "CiscoiNode"{
> # match if option vendor-class-identifier="Cisco.iNode.oib.1.0";
> # option iNode-manager 01:04:0a:7b:00:0a;
> # option tftp-server-name "10.123.0.9";
> # option bootfile-name "inode.bin";
> # option domain-name "inode.sectv.com <http://inode.sectv.com/>";
> # }
> }
>
> # 10.123.4.56/29 Subnet
> subnet 10.123.4.56 netmask 255.255.255.248 {
> range 10.123.4.58 10.123.4.62;
> option subnet-mask 255.255.255.248;
> option domain-search "sectv.com <http://sectv.com/>";
> option routers 10.123.4.57;
> option broadcast-address 10.123.4.63;
> }
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