Проверка работы dhcp сервера linux
Monitoring DHCP usage on linux seems, to me, to be kind of clumsy.
While I am not a Windows Server fan, it was fairly easy to extract DHCP information. Each night I had a process that extracted the DHCP information from the Windows DHCP server, and post everything to a MySQL database.
The DHCP data was accessed with a simple CGI script so I could quickly and easily ascertain anything I needed to know regarding DHCP assignments. I could locate all MACs ever assigned to an IP address, the current IP address for a hostname, all of the IP/MACs at a branch, etc. It was sweet.
Going through the trouble to extract data on that network, with 10,000+ users, made sense. On my home system, it doesn’t. So every six months, or so, when I need to figure out a DHCP issue I end up flailing trying to remember what to do.
After this morning’s flail, I decided to write some notes down so I don’t have to flail again.
Monitoring DHCP Packets
My home DHCP server is a Raspberry Pi. Yep, and it works really quite nicely. See here for the setup. Normally, if I want to watch DHCP packets I either end up running tcpdump or WireShark on the Raspberry pi. Today I stumbled across dhcpdump which is like tcpdump, except all it does is dump formatted DHCP packets for you, so you don’t have to remember the exact DHCP packet format for tcpdump.
My RPI didn’t have dhcpdump installed, but it was easy to add:
apt-get update apt-get install dhcpdump
dhcpdump uses tcpdump, so if you don’t have tcpdump installed, it will get installed.
To run dhcpdump, you just have to specify the interface you want to monitor. This is probably going to be eth0, but you can use ifconfig to verify:
Here is an example of a dhcp request and response:
TIME: 2015-01-02 12:36:20.502 IP: 191.0.10.110 (1c:3e:84:b9:14:19) > 255.255.255.255 (ff:ff:ff:ff:ff:ff) OP: 1 (BOOTPREQUEST) HTYPE: 1 (Ethernet) HLEN: 6 HOPS: 0 XID: 7f8ffaa2 SECS: 0 FLAGS: 0 CIADDR: 191.0.10.110 YIADDR: 0.0.0.0 SIADDR: 0.0.0.0 GIADDR: 0.0.0.0 CHADDR: 1c:3e:84:b9:14:19:00:00:00:00:00:00:00:00:00:00 SNAME: . FNAME: . OPTION: 53 ( 1) DHCP message type 8 (DHCPINFORM) OPTION: 61 ( 7) Client-identifier 01:1c:3e:84:b9:14:19 OPTION: 12 ( 8) Host name latidude OPTION: 60 ( 8) Vendor class identifier MSFT 5.0 OPTION: 55 ( 13) Parameter Request List 1 (Subnet mask) 15 (Domainname) 3 (Routers) 6 (DNS server) 44 (NetBIOS name server) 46 (NetBIOS node type) 47 (NetBIOS scope) 31 (Perform router discovery) 33 (Static route) 121 (Classless Static Route) 249 (MSFT - Classless route) 43 (Vendor specific info) 252 (MSFT - WinSock Proxy Auto Detec t) --------------------------------------------------------------------------- TIME: 2015-01-02 12:36:20.503 IP: 191.0.10.15 (b8:27:eb:22:87:65) > 191.0.10.110 (1c:3e:84:b9:14:19) OP: 2 (BOOTPREPLY) HTYPE: 1 (Ethernet) HLEN: 6 HOPS: 0 XID: 7f8ffaa2 SECS: 0 FLAGS: 0 CIADDR: 191.0.10.110 YIADDR: 0.0.0.0 SIADDR: 0.0.0.0 GIADDR: 0.0.0.0 CHADDR: 1c:3e:84:b9:14:19:00:00:00:00:00:00:00:00:00:00 SNAME: . FNAME: . OPTION: 53 ( 1) DHCP message type 5 (DHCPACK) OPTION: 54 ( 4) Server identifier 191.0.10.15 OPTION: 1 ( 4) Subnet mask 255.255.255.0 OPTION: 15 ( 11) Domainname flipflop.net OPTION: 3 ( 4) Routers 191.0.10.1 OPTION: 6 ( 4) DNS server 191.0.10.15 OPTION: 44 ( 4) NetBIOS name server 191.0.10.15 OPTION: 46 ( 1) NetBIOS node type 8 (H-node) ---------------------------------------------------------------------------
Script To Examine Current DHCP Lease Status
Often I want to know what leases are active, and who are using them. There seems to be no utility for doing this. Instead, I have to manually look thru the /var/lib/dhcp/dhcpd.leases file. Because I only look at this thing maybe once every 6 months, inevitably it takes me to long to find what I’m looking for.
I wrote the following script which will parse the dhcpd.leases file and create a single line of information for each IP address in the format:
IP Addr Status MAC Host Name 191.0.10.200 free f8:b1:56:a2:07:fc 191.0.10.218 free 08:00:27:43:b4:01 191.0.10.220 free 08:00:27:66:0b:e9 191.0.10.221 free 08:00:27:ab:8b:d2
This tells you the status of each IP address. The current (or last) MAC address assigned, and a host name, if available.
Here is the script (I call mine showdhcp):
#!/bin/bash echo "You must run this script with root privileges" echo # get a valid temporary file name tempFile=$(mktemp) # extract just the useful lines from the dhcpd.leases file cat /var/lib/dhcp/dhcpd.leases \ | grep \ -e '^lease ' \ -e '^ binding state' \ -e hardware \ -e client-hostname \ -e > >$tempFile.1 # remove superflous text from each linE sed -e "s/^lease \(.*\) //" \ $tempFile.1 > $tempFile.2 # join the lines so that each lease is on a single line, then sorT sed -e ":'loop';/~$/N;s/~\n/,/;t'loop'" \ -e "s/,$//" \ -e "s/,/\t/g" \ $tempFile.2 | sort > $tempFile.3 # delete duplicate lines sed -e'$!N;/^\(.*\)\n\1$/!P;D' $tempFile.3 > $tempFile.4 printf "IP Addr\t\tStatus\tMAC\t\t\tHost Name\n" cat $tempFile.4 rm $tempFile.*
Hey! That’s the most I done with SED in years!
Here is a full sample output:
root@ns:~# ./showdhcp You must run this script with root privileges IP Addr Status MAC Host Name 191.0.10.200 free f8:b1:56:a2:07:fc 191.0.10.218 free 08:00:27:43:b4:01 191.0.10.220 free 08:00:27:66:0b:e9 191.0.10.221 free 08:00:27:ab:8b:d2 191.0.10.222 free b8:27:eb:5d:44:21 191.0.10.223 free 00:c1:40:49:0e:11 191.0.10.224 free 08:00:27:c8:16:45 191.0.10.225 free 00:21:9b:17:37:ab 191.0.10.226 free 80:1f:02:f6:7a:06 191.0.10.227 free 00:1d:92:4a:c3:43 191.0.10.229 free 00:11:11:ae:a6:1c 191.0.10.230 free 08:00:27:bf:90:9f 191.0.10.231 free f4:f1:e1:b2:de:4f 191.0.10.232 free 00:50:43:00:9c:64 191.0.10.233 active 00:50:c2:77:42:60 "GS100531" 191.0.10.234 free 3c:43:8e:de:fb:aa 191.0.10.235 free 7c:ed:8d:ea:44:f3 191.0.10.236 free 00:21:9b:17:37:ab 191.0.10.237 free 1c:3e:84:b9:14:19 191.0.10.238 free 64:66:b3:1b:89:02 191.0.10.239 free 1c:3e:84:b9:14:19 191.0.10.240 free 30:f9:ed:7f:d0:0e 191.0.10.241 free 00:18:56:24:72:79 191.0.10.242 free 08:00:27:ff:ab:fd 191.0.10.243 free 00:21:2f:2e:be:72 191.0.10.244 free 00:11:11:61:fc:5f 191.0.10.245 free 80:1f:02:b5:b3:80 191.0.10.246 free 00:11:11:61:fc:5f 191.0.10.247 free 90:a2:da:0d:02:6b 191.0.10.248 free f8:b1:56:a2:07:fc 191.0.10.249 free a4:1f:72:6d:83:64 191.0.10.250 free 00:23:99:1d:8e:49 191.0.10.251 active f8:e0:79:ca:b9:d6 "android-bb86746386c86c4f" 191.0.10.252 free 08:00:27:c8:16:45 191.0.10.253 active 00:1d:fe:e0:1c:ff 191.0.10.254 free 08:00:27:30:83:23
Установка и базовая настройка DHCP сервера на Ubuntu
Опубликовано: 12.03.2023
Установка и настройка
Сервер DHCP в Ubuntu может быть реализован с помощью пакета isc-dhcp-server. Его можно установить из стандартных репозиториев системы. Выполняем обновления кэша пакетов и установку:
subnet 192.168.0.0 netmask 255.255.255.0 <
range 192.168.0.100 192.168.0.200;
option domain-name-servers 192.168.0.10, 192.168.0.11;
option domain-name «dmosk.local»;
option routers 192.168.0.1;
option broadcast-address 192.168.0.255;
default-lease-time 600;
max-lease-time 7200;
>
- subnet — сеть, для которой будет работать данная группа настроек.
- range — диапазон, из которого будут браться IP-адреса.
- option domain-name-servers — через запятую перечисленные DNS-сервера.
- option domain-name — суффикс доменного имени.
- option routers — шлюз по умолчанию.
- option broadcast-address — адрес сети для широковещательных запросов.
- default-lease-time и max-lease-time — время и максимальное время в секундах, на которое клиент получит адрес, по его истечению будет выполнено продление срока.
Проверить корректность конфигурационного файла можно командой:
dhcpd -t -cf /etc/dhcp/dhcpd.conf
Разрешаем автозапуск сервиса:
systemctl enable isc-dhcp-server
systemctl restart isc-dhcp-server
Добавляем правило в firewall:
iptables -I INPUT -p udp —dport 67 -j ACCEPT
Возможные проблемы
Not configured to listen on any interfaces!
Сервис dhcp не запускается, а в логе можно увидеть ошибки, на подобие:
No subnet declaration for ens18 (192.168.1.10).
.
** Ignoring requests on ens18. If this is not what
you want, please write a subnet declaration
in your dhcpd.conf file for the network segment
to which interface ens18 is attached. **
.
Not configured to listen on any interfaces
Причина: в конфигурационном файле описана подсеть, которая не настроена ни на одном из сетевых интерфейсов сервера.
Решение: конфигурация subnet должна включать только те подсети, в которых настроен сам сервер DHCP. Посмотреть сетевые настройки можно командой:
После чего необходимо проверить настройки в конфигурационном файле сервера dhcp.
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