diff --git a/asyncreadline.nim b/asyncutils.nim
similarity index 50%
rename from asyncreadline.nim
rename to asyncutils.nim
index 7990262..36d23a8 100644
--- a/asyncreadline.nim
+++ b/asyncutils.nim
@@ -1,7 +1,6 @@
+import asyncdispatch, threadpool, osproc
+
 ## asyncReadline as discussed at https://github.com/nim-lang/Nim/issues/11564
-
-import asyncdispatch, threadpool
-
 proc asyncReadline*(): Future[string] =
   let event = newAsyncEvent()
   let future = newFuture[string]("asyncReadline")
@@ -15,4 +14,15 @@ proc asyncReadline*(): Future[string] =
   addEvent(event, callback)
   return future
 
-
+proc asyncExecCmd*(command: string): Future[int] =
+  let event = newAsyncEvent()
+  let future = newFuture[int]("asyncExecCmd")
+  proc execCmdBackground(event: AsyncEvent, command: string): int =
+    result = execCmd(command)
+    event.trigger()
+  let flowVar = spawn execCmdBackground(event, command)
+  proc callback(fd: AsyncFD): bool =
+    future.complete(^flowVar)
+    true                                                                                
+  addEvent(event, callback)
+  return future
diff --git a/punch.nim b/punch.nim
index 16c966c..7231146 100644
--- a/punch.nim
+++ b/punch.nim
@@ -1,7 +1,9 @@
 import
   asyncdispatch,
+  asyncutils,
   network_interface,
-  packet_info
+  packet_info,
+  strformat
 
 from nativesockets import SOCK_RAW, bindAddr, htons
 from posix import ioctl, setsockopt, SockAddr, SockLen, SocketHandle
@@ -35,38 +37,38 @@ var
   PACKET_ADD_MEMBERSHIP {.importc: "PACKET_ADD_MEMBERSHIP", header: "<linux/if_packet.h>".}: cushort
   PACKET_MR_PROMISC {.importc: "PACKET_MR_PROMISC", header: "<linux/if_packet.h>".}: cushort
 
-proc punchHoleAsClient*(clientAddress: string,
-                        clientPort: Port,
-                        serverAddress: string,
-                        serverPort: Port) {.async.} =
-  echo "punchHoleAsClient"
+proc setupRawSocket(iface: NetworkInterface): AsyncFD =
   # Create a raw packet socket. For accessing outgoing packets we need to use
   # ETH_P_ALL which is needed in network byte order, see packet(7) man page.
-  let rawFd = createAsyncNativeSocket(AF_PACKET.cint,
-                                      SOCK_RAW.cint,
-                                      htons(ETH_P_ALL).cint)
+  result = createAsyncNativeSocket(AF_PACKET.cint,
+                                   SOCK_RAW.cint,
+                                   htons(ETH_P_ALL).cint)
 
   # Limit capturing of packets to the desired network interface, see
   # netdevice(7) man page
-  let iface = fromIpAddress(clientAddress)
   echo "interface: ", iface.name, ", index: ", iface.index
   var sa = Sockaddr_ll(sll_family: AF_PACKET,
                        sll_protocol: htons(ETH_P_ALL),
                        sll_ifindex: iface.index)
-  if bindAddr(rawFd.SocketHandle,
+  if bindAddr(result.SocketHandle,
               cast[ptr SockAddr](addr sa),
               sizeof(Sockaddr_ll).SockLen) != 0:
     raise newException(PunchHoleError, "cannot bind to interface")
   
   # Enable promiscuous mode, see netdevice(7) man page
   var req = Packet_mreq(mr_ifindex: iface.index, mr_type: PACKET_MR_PROMISC)
-  if setsockopt(rawFd.SocketHandle,
+  if setsockopt(result.SocketHandle,
                 SOL_PACKET.cint,
                 PACKET_ADD_MEMBERSHIP.cint,
                 addr req,
                 sizeof(req).SockLen) != 0:
     raise newException(PunchHoleError, "cannot enable promiscuous mode")
 
+proc captureSequenceNumber(rawFd: AsyncFD,
+                           clientAddress: string,
+                           clientPort: Port,
+                           serverAddress: string,
+                           serverPort: Port): Future[uint32] {.async.} =
   while true:
     let packet = await rawFd.recv(4000)
     if packet == "":
@@ -78,8 +80,61 @@ proc punchHoleAsClient*(clientAddress: string,
        packetInfo.tcpPortSrc.int == clientPort.int and
        packetInfo.tcpIpDst == serverAddress and
        packetInfo.tcpPortDst.int == serverPort.int:
-      echo "captured packet, sequence number: ", packetInfo.tcpSeqNumber
-      break
+      return packetInfo.tcpSeqNumber
 
+proc addFirewallRule(clientAddress: string,
+                     clientPort: Port,
+                     serverAddress: string,
+                     serverPort: Port) {.async.} =
+  let firewall_cmd = fmt"""iptables -A INPUT \
+  -d {clientAddress} \
+  -p icmp \
+  --icmp-type time-exceeded \
+  -m conntrack \
+  --ctstate RELATED \
+  --ctproto tcp \
+  --ctorigsrc {clientAddress} \
+  --ctorigsrcport {clientPort.int} \
+  --ctorigdst {serverAddress} \
+  --ctorigdstport {serverPort.int} \
+  -j DROP"""
+  let exitcode = await asyncExecCmd(firewall_cmd)
+  if exitcode != 0:
+    raise newException(PunchHoleError, "cannot add firewall rule")
+
+proc deleteFirewallRule(clientAddress: string,
+                        clientPort: Port,
+                        serverAddress: string,
+                        serverPort: Port) {.async.} =
+  let firewall_cmd = fmt"""iptables -D INPUT \
+  -d {clientAddress} \
+  -p icmp \
+  --icmp-type time-exceeded \
+  -m conntrack \
+  --ctstate RELATED \
+  --ctproto tcp \
+  --ctorigsrc {clientAddress} \
+  --ctorigsrcport {clientPort.int} \
+  --ctorigdst {serverAddress} \
+  --ctorigdstport {serverPort.int} \
+  -j DROP"""
+  let exitcode = await asyncExecCmd(firewall_cmd)
+  if exitcode != 0:
+    raise newException(PunchHoleError, "cannot delete firewall rule")
+
+proc punchHoleAsClient*(clientAddress: string,
+                        clientPort: Port,
+                        serverAddress: string,
+                        serverPort: Port) {.async.} =
+  let iface = fromIpAddress(clientAddress)
+  let rawFd = setupRawSocket(iface)
+  let seqNumber = await captureSequenceNumber(rawFd,
+                                              clientAddress,
+                                              clientPort,
+                                              serverAddress,
+                                              serverPort)
+  echo "captured sequence number: ", seqNumber
+  await addFirewallRule(clientAddress, clientPort, serverAddress, serverPort)
+  await deleteFirewallRule(clientAddress, clientPort, serverAddress, serverPort)
   closeSocket(rawFd)
 
diff --git a/syni_prototype.nim b/syni_prototype.nim
index 33319e6..b050d89 100644
--- a/syni_prototype.nim
+++ b/syni_prototype.nim
@@ -2,7 +2,7 @@ import
   net,
   asyncnet,
   asyncdispatch,
-  asyncreadline,
+  asyncutils,
   punch
 
 from strutils import format, join