Mikrotik/RouterOS can't handle very well /32 on Point-to-Point links (like GRE). There is a separate howto to explain how to setup /32 between in a GRE link (or even a OpenVPN). What is the easy way? Just use any /30 on the GRE Link, either from your assigned DN42 pool address or use a private address like 192.168. Please don't choose from 172.16.0.0/12 or 10.0.0.0/8 because they may overlap with DN42 or ChaosVPN.
First, let's add IPSec peer and encryption policy.
Peer most likely provided you with encryption details.
If not, ask them about it. Here we're gonna use aes256-sha256-modp1536
/ip ipsec peer add address=188.8.131.52 comment=gre-dn42-peer dh-group=modp1536 \ enc-algorithm=aes-256 hash-algorithm=sha256 local-address=184.108.40.206 secret=PASSWORD
/ip ipsec policy add comment=gre-dn42-peer dst-address=220.127.116.11/32 proposal=dn42 protocol=gre \ sa-dst-address=18.104.22.168 sa-src-address=22.214.171.124 src-address=126.96.36.199/32
Pretty straightforward here
/interface gre add allow-fast-path=no comment="DN42 somepeer" local-address=188.8.131.52 name=gre-dn42-peer \ remote-address=184.108.40.206
Your peer most likely provided you with IP adresses for GRE tunnel.
As I said before, you can't use /31 for PtP links, so, in the "easy way" we will be using /30. If you want to avoid wasting a whole /30 for your peering, please check the point-to-point configuration for RouterOS
Add the IP your peer provided you:
/ip address add address=192.168.200.130/30 interface=gre-dn42-peer network=192.168.200.128
Here we can use /127, so it's simple:
/ipv6 address add address=fdc8:c633:5319:3300::41/127 advertise=no interface=gre-dn42-peer
If you configured everything correctly, you should be able to ping
It's a good idea to setup filters for BGP instances, both IN (accept advertises) and OUT (send advertises)
In this example, we will be filtering IN: 192.168.0.0/16 and 169.254.0.0/16
OUT: 192.168.0.0/16 and 169.254.0.0/16, you really don't want to advertise this networks.
This filter will not only catch /8 or /16 networks, but smaller networks inside this subnets as well.
/routing filter add action=discard address-family=ip chain=dn42-in prefix=192.168.0.0/16 prefix-length=16-32 protocol=bgp add action=discard address-family=ip chain=dn42-in prefix=169.254.0.0/16 prefix-length=16-32 protocol=bgp add action=discard address-family=ip chain=dn42-out prefix=192.168.0.0/16 prefix-length=16-32 protocol=bgp add action=discard address-family=ip chain=dn42-out prefix=169.254.0.0/16 prefix-length=16-32 protocol=bgp
Now, if you want only DN42 connection, you can filter IN 10.0.0.0/8 (ChaosVPN / freifunk networks):
/routing filter add action=discard address-family=ip chain=dn42-in prefix=10.0.0.0/8 prefix-length=8-32 protocol=bgp
Now, for actual BGP configuration.
Let's add some peers. Right now we have just one, but we still need two connections - to IPv4 and IPv6
/routing bgp instance set default disabled=yes add as=YOUR_AS client-to-client-reflection=no name=bgp-dn42-somename out-filter=dn42-in \ router-id=220.127.116.11
IPv6 (if needed):
/routing bgp peer add comment="DN42: somepeer IPv4" in-filter=dn42-in instance=bgp-dn42-somename multihop=yes \ name=dn42-somepeer-ipv4 out-filter=dn42-out remote-address=192.168.200.129 remote-as=PEER_AS \ route-reflect=yes ttl=default
/routing bgp peer add address-families=ipv6 comment="DN42: somepeer IPv6" in-filter=dn42-in \ instance=bgp-dn42-somename multihop=yes name=dn42-somepeer-ipv6 out-filter=dn42-out \ remote-address=fd42:c644:5222:3222::40 remote-as=PEER_AS route-reflect=yes ttl=default
Also, as a note, Mikrotik doesn't deal well with BGP running over link-local addresses (the address starting with fe80). You need to use a fd42:: address in your BGP session, otherwise, BGP will not install any received route.
You want to advertise your allocated network (most likely), it's very simple:
You can repeat that with as much IPv4 and IPv6 networks which you own.
/routing bgp network add network=YOUR_ALLOCATED_SUBNET synchronize=no
Separate dns requests for dn42 tld from your default dns traffic with L7 filter in Mikrotik. Change network and LAN GW to mach your network configuration.
Since version 6.47 have added functionality that can redirect DNS queries according to special rules. If you used to do Layer-7 rules in the firewall, now it's simple and elegant:
/ip firewall layer7-protocol add name=DN42-DNS regexp="\\x04dn42.\\x01" /ip firewall nat add action=src-nat chain=srcnat comment="NAT to DN42 DNS" dst-address=172.23.0.53 dst-port=53 protocol=udp src-address=192.168.0.0/24 to-addresses=192.168.0.1 add action=dst-nat chain=dstnat dst-address-type=local dst-port=53 layer7-protocol=DN42-DNS protocol=udp src-address=192.168.0.0/24 to-addresses=172.23.0.53 to-ports=53
/ip dns static add comment=DN42 forward-to=172.23.0.53 regexp=".*\\.dn42" type=FWD