this post was submitted on 24 Jun 2023
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Hi!

I'm trying to make a DIY router. I used configs from some online guides (the nftables one is from the project's website), but nothing happens when I connect a different machine. I know that description doesn't say much, so I'd like to know how can I check what's actually wrong. My system (Guix) config is below:

(use-modules (gnu))
(use-service-modules cups desktop networking ssh xorg sysctl linux dns)

(define wan "enp0s29u1u5")

(define lan "enp0s25")

(define dnsmasq-config
  "# Listen on this specific port instead of the standard DNS port
# (53). Setting this to zero completely disables DNS function,
# leaving only DHCP and/or TFTP.
port=53
# Never forward plain names (without a dot or domain part)
domain-needed
# Never forward addresses in the non-routed address spaces.
bogus-priv
# By  default,  dnsmasq  will  send queries to any of the upstream
# servers it knows about and tries to favour servers to are  known
# to  be  up.  Uncommenting this forces dnsmasq to try each query
# with  each  server  strictly  in  the  order  they   appear   in
# /etc/resolv.conf
strict-order
# Set this (and domain: see below) if you want to have a domain
# automatically added to simple names in a hosts-file.
expand-hosts
# Set the domain for dnsmasq. this is optional, but if it is set, it
# does the following things.
# 1) Allows DHCP hosts to have fully qualified domain names, as long
#     as the domain part matches this setting.
# 2) Sets the \"domain\" DHCP option thereby potentially setting the
#    domain of all systems configured by DHCP
# 3) Provides the domain part for \"expand-hosts\"
#domain=thekelleys.org.uk
domain=example.com

# Set Listen address
listen-address=127.0.0.1 # Set to Server IP for network responses

dhcp-range=192.168.3.25,192.168.3.50,24h
dhcp-option=option:router,192.168.3.1
dhcp-option=option:ntp-server,192.168.3.5
dhcp-option=option:dns-server,192.168.3.5
dhcp-option=option:netmask,255.255.255.0
")

(define nftables-config
  (format #f
	  "flush ruleset

define DEV_PRIVATE = ~a
define DEV_WORLD = ~a
define NET_PRIVATE = 192.168.0.0/16

table ip global {

    chain inbound_world {
        # accepting ping (icmp-echo-request) for diagnostic purposes.
        # However, it also lets probes discover this host is alive.
        # This sample accepts them within a certain rate limit:
        #
        # icmp type echo-request limit rate 5/second accept

        # allow SSH connections from some well-known internet host
        ip saddr 81.209.165.42 tcp dport ssh accept
    }

    chain inbound_private {
        # accepting ping (icmp-echo-request) for diagnostic purposes.
        icmp type echo-request limit rate 5/second accept

        # allow DHCP, DNS and SSH from the private network
        ip protocol . th dport vmap { tcp . 22 : accept, udp . 53 : accept, tcp . 53 : accept, udp . 67 : accept}
    }

    chain inbound {
        type filter hook input priority 0; policy drop;

        # Allow traffic from established and related packets, drop invalid
        ct state vmap { established : accept, related : accept, invalid : drop }

        # allow loopback traffic, anything else jump to chain for further evaluation
        iifname vmap { lo : accept, $DEV_WORLD : jump inbound_world, $DEV_PRIVATE : jump inbound_private }

        # the rest is dropped by the above policy
    }

    chain forward {
        type filter hook forward priority 0; policy drop;

        # Allow traffic from established and related packets, drop invalid
        ct state vmap { established : accept, related : accept, invalid : drop }

        # connections from the internal net to the internet or to other
        # internal nets are allowed
        iifname $DEV_PRIVATE accept

        # the rest is dropped by the above policy
    }

    chain postrouting {
        type nat hook postrouting priority 100; policy accept;

        # masquerade private IP addresses
        ip saddr $NET_PRIVATE oifname $DEV_WORLD masquerade
    }
}
" lan wan))

(operating-system
 (locale "en_GB.utf8")
 (timezone "Europe/Warsaw")
 (keyboard-layout (keyboard-layout "pl" "legacy" #:options '("ctrl:nocaps")))
 (host-name "router")

 (kernel-arguments
  (list
   "modprobe.blacklist=pcspkr,snd_pcsp"))
 
 ;; The list of user accounts ('root' is implicit).
 (users (cons* (user-account
                (name "formbi")
                (comment "Formbi")
                (group "users")
                (home-directory "/home/formbi")
                (supplementary-groups '("wheel" "netdev" "audio" "video")))
               %base-user-accounts))

 ;; Packages installed system-wide.  Users can also install packages
 ;; under their own account: use 'guix search KEYWORD' to search
 ;; for packages and 'guix install PACKAGE' to install a package.
 (packages
  (append (list (specification->package "nss-certs"))
                   %base-packages))

 ;; Below is the list of system services.  To search for available
 ;; services, run 'guix system search KEYWORD' in a terminal.
 (services
  (append (list
	   (service xfce-desktop-service-type)
	   (service guix-publish-service-type
		    (guix-publish-configuration
		     (port 2137)
		     (advertise? #t)))
	   (service earlyoom-service-type
		    (earlyoom-configuration
		     (avoid-regexp "emacs")
		     (minimum-available-memory 5)
		     (minimum-free-swap 20)))

           (service openssh-service-type)
           (service cups-service-type)

	   (service dnsmasq-service-type)

	   (extra-special-file "/etc/dnsmasq.conf"
			       (plain-file "dnsmasq.conf" dnsmasq-config))

	   (service nftables-service-type
		    (nftables-configuration
		     (ruleset (plain-file "nftables.conf" nftables-config))))


	   (set-xorg-configuration
            (xorg-configuration (keyboard-layout keyboard-layout))))

          ;; This is the default list of services we
          ;; are appending to.
	  (modify-services
	   %desktop-services
	   
	   (sysctl-service-type
	    config =>
	    (sysctl-configuration
	     (settings (append '(("vm.swappiness" . "10")
				 ("net.ipv4.ip_forward" . "1"))
			       %default-sysctl-settings))))

	   (network-manager-service-type
	    config =>
	    (network-manager-configuration
					;(dns "dnsmasq")
	     ))
	   
	   (guix-service-type
	    config =>
	    (guix-configuration
	     (discover? #t))))))
 
 (bootloader (bootloader-configuration
              (bootloader grub-bootloader)
              (targets (list "/dev/sda"))
              (keyboard-layout keyboard-layout)))
 (swap-devices (list (swap-space
                      (target (uuid
                               "a32aa366-c966-460f-9592-2a08c5cad947")))))

 ;; The list of file systems that get "mounted".  The unique
 ;; file system identifiers there ("UUIDs") can be obtained
 ;; by running 'blkid' in a terminal.
 (file-systems (cons* (file-system
                       (mount-point "/")
                       (device (uuid
                                "30b3a834-f23e-42ad-addf-0cde5538a96f"
                                'ext4))
                       (type "ext4")) %base-file-systems)))
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[–] lack 2 points 1 year ago (1 children)

Take it from the bottom up:

Step 1: look at ip link show on both sides. If they have NO_CARRIER, check your cable.

Step 2: Look at ip address show on both sides. Do they both have one? Do the subnets and masks match?

Step 2a: Is the client side configured to be up and ask for a DHCP address? Is Dnsmasq actually running on the server side? is it listening in the right interface?

Step 2b: use tcpdump -ttt -e -i eth0 on both sides to watch for packets. Do you see DHCP or bootp requests coming from the client? do you see responses coming from the server?

Step 3: Look at ip route show in the client. Is the default route correct? Is it the router's IP? Can you ping the default route? Is DNS configured and working?

Step 4: look at your nftables. do you have NAT set up right? look at tcpdump on the client and both sides of the router. when the client tries to get to the internet, do you see packets go all the way out and all the way back?

[–] [email protected] 1 points 1 year ago (1 children)

thanks for your response!

1: the cable was indeed bad (it was brand new, so I wasn't suspecting it), but something else is still wrong

2: sorry for just pasting, I'm not really sure how to interpret it client:

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope global lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether f0:de:f1:5d:57:0c brd ff:ff:ff:ff:ff:ff
    inet6 fe80::29d:f28a:75a7:b5ab/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever
3: wlp3s0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default qlen 1000
    link/ether e2:a8:25:b3:ef:1a brd ff:ff:ff:ff:ff:ff permaddr 00:24:d7:a6:ce:e4
4: docker0: <NO-CARRIER,BROADCAST,MULTICAST,UP> mtu 1500 qdisc noqueue state DOWN group default 
    link/ether 02:42:0f:11:f5:37 brd ff:ff:ff:ff:ff:ff
    inet 172.17.0.1/16 brd 172.17.255.255 scope global docker0
       valid_lft forever preferred_lft forever

server:

1: lo: <LOOPBACK,MULTICAST,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1000
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope global lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
3: enp0s25: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 6e:10:39:1a:0b:03 brd ff:ff:ff:ff:ff:ff
    inet6 fe80::2721:8559:a60d:2e65/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever
4: enp0s29u1u5: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UNKNOWN group default qlen 1000
    link/ether 02:48:11:4d:31:03 brd ff:ff:ff:ff:ff:ff
    inet 192.168.167.220/24 brd 192.168.167.255 scope global dynamic noprefixroute enp0s29u1u5
       valid_lft 3540sec preferred_lft 3540sec
    inet6 fe80::6c7f:73bd:fb6c:bacd/64 scope link noprefixroute 
       valid_lft forever preferred_lft forever

2a: I'm using network manager, it has worked so far. When I try to connect to the wired network manually (normally it does it automatically), nmtui says Could not activate connection: Activation failed: IP configuration could not be reserved (no available address, timeout, etc.). Dnsmasq is running, but I don't know hot to check where is't listening (I tried looking it up, but didn't find anything).

2b: http://ix.io/4z3X/text

3: it only shows the dummy docker thing; when I connect to the wi-fi hotspot in my phone, it does appear and I can ping it

4: I'm not sure, the nftables config is pasted in the original post

[–] lack 1 points 1 year ago

The first thing I noticed was that your servers "lan" interface has no IPv4 address. Compare the section for enp0s25 to that of your wan port... notice how the inet line is missing.

Based on your dnsmasq config I assume you'd want the server to have a static IP of 192.168.3.1

Dnsmasq is also going to configure the client with the DNS server and NTP set 192.168.3.5. Is this another machine in your network already, or is that a typo?