Manual:PCC: Difference between revisions

From MikroTik Wiki
Jump to navigation Jump to search
← Older editNewer edit →
Megis (talk | contribs)
470 edits
Megis (talk | contribs)
470 edits
No edit summary
Line 46: Line 46:
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/1 \
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/1 \
     action=mark-connection new-connection-mark=wlan2_conn passthrough=yes
     action=mark-connection new-connection-mark=wlan2_conn passthrough=yes
add chain=prerouting connection-mark=wlan1_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan1 passthrough=yes
add chain=prerouting connection-mark=wlan1_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan1
add chain=prerouting connection-mark=wlan2_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan2 passthrough=yes
add chain=prerouting connection-mark=wlan2_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan2


/ ip route
/ ip route
Line 59: Line 59:
add chain=srcnat out-interface=wlan2 action=masquerade
add chain=srcnat out-interface=wlan2 action=masquerade
</pre>
</pre>




Line 79: Line 73:
The LAN interface has the name "Local" and IP address of 192.168.0.1/24.
The LAN interface has the name "Local" and IP address of 192.168.0.1/24.


===Policy routing===


===NAT===
First it is necessary to take care of router's traffic - we need to make sure that traffic will leave via same interface it was coming from.
We will mark all incoming connections, to remember what was the interface.
<pre>
<pre>
/ ip firewall nat
/ ip firewall mangle
add chain=srcnat out-interface=wlan1 action=masquerade
add chain=input in-interface=wlan1 action=mark-connection new-connection-mark=wlan1_conn
add chain=srcnat out-interface=wlan2 action=masquerade
add chain=input in-interface=wlan2 action=mark-connection new-connection-mark=wlan2_conn
</pre>
</pre>
 
Then we will assign proper routing-mark to the packets leaving the router.  
As routing decision is already made we just need rules that will fix src-addresses for all outgoing packets. if this packet will leave via wlan1 it will be NATed to 10.112.0.2/24,
if via wlan2 then NATed to 10.111.0.2/24 
 
 
===Routing===
<pre>
<pre>
/ ip route
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla1   
add dst-address=0.0.0.0/0 gateway=10.111.0.1,10.112.0.1 check-gateway=ping
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla2
</pre>
</pre>


This is typical ECMP (Equal Cost Multi-Path) gateway with check-gateway. ECMP is "persistent per-connection load balancing" or "per-src-dst-address combination load balancing".
Action mark-routing can be used only in mangle chain '''output''' and '''prerouting''', but mangle chain '''prerouting''' is capturing all traffic that is going to the router itself.
As soon as one of the gateway will not be reachable, check-gateway will remove it from gateway list. And you will have a "failover" effect.
To avoid this we will use ''dst-address-type=!local''. And with the help of the new PCC we will devide traffic into two groups based on source and destination addressees.
 


You can use asymmetric bandwidth links also  - for example one link is 2Mbps other 10Mbps. Just use this command to make load balancing 1:5
<pre>    
<pre>
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/0 \
/ ip route
    action=mark-connection new-connection-mark=wlan1_conn passthrough=yes
add dst-address=0.0.0.0/0 gateway=10.111.0.1,10.112.0.1,10.112.0.1,10.112.0.1,10.112.0.1,10.112.0.1 check-gateway=ping
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/1 \
    action=mark-connection new-connection-mark=wlan2_conn passthrough=yes
</pre>
</pre>


===Connections to the router itself===
Then we need to mark all packets from those connections with a proper mark. As policy routing is required ponly for traffic going to the Internet, do not forget to specify in-interface option.


<pre>
<pre>
/ ip firewall mangle
add chain=prerouting connection-mark=wlan1_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan1
add chain=input in-interface=wlan1 action=mark-connection new-connection-mark=wlan1_conn
add chain=prerouting connection-mark=wlan2_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan2
add chain=input in-interface=wlan2 action=mark-connection new-connection-mark=wlan2_conn
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wlan1    
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wlan2    
</pre>
</pre>


Create a route for each routing-mark
<pre>
<pre>
/ ip route
/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 routing-mark=to_wlan1
add dst-address=0.0.0.0/0 gateway=10.111.0.1 routing-mark=to_wla1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.111.0.2 routing-mark=to_wlan2
add dst-address=0.0.0.0/0 gateway=10.112.0.1 routing-mark=to_wla2 check-gateway=ping
</pre>
</pre>


With all multi-gateway situations there is a usual problem to reach router from public network via one, other or both gateways. Explanations is very simple -  
To enable failover, it is necessary to have a routes that will jump in as soon as others will become inactive on gateway failure. (and that will happen only if check-gateway option is active)
Outgoing packets uses same routing decision as packets that are going trough the router. So reply to a packet that was received via wlan1 might be send out and masqueraded via wlan2.
<pre>
add dst-address=0.0.0.0/0 gateway=10.111.0.1 distance=1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 distance=2 check-gateway=ping
</pre>


To avoid that we need to policy routing those connections.
===NAT===
As routing decision is already made we just need rules that will fix src-addresses for all outgoing packets. if this packet will leave via wlan1 it will be NATed to 10.112.0.2/24,
if via wlan2 then NATed to 10.111.0.2/24 


==Known Issues==
<pre>
 
/ ip firewall nat
===DNS issues===
add chain=srcnat out-interface=wlan1 action=masquerade
 
add chain=srcnat out-interface=wlan2 action=masquerade
ISP specific DNS servers might have custom configuration that treats specific requests from ISP's network differently than requests from other network. So in case connection is made via other gateway those sites will not be accessible.
</pre>
 
To avoid that we suggest to use 3rd-party (public) DNS servers, and in case you need ISP specific recourse, create static DNS entry and policy route that traffic to specific gateway.
 
===Routing table flushing===
 
Every time when something triggers flush of the routing table and ECMP cache is flushed. Connections will be assigned to gateways once again and may or may not be on the same gateway.(in case of 2 gateways there are 50% chance that traffic will start to flow via other gateway).
 
 
If you have fully routed network (clients address can be routed via all available gateway), change of the gateway will have no ill effect, but in case you use
masquerade, change of the gateway will result in change of the packet's source address and connection will be dropped.
 
 
Routing table flush can be caused by  2 things:
 
1) routing table change  (dynamic routing protocol update, user manual changes)
 
2) every 10 minutes routing table is flushed for security reasons (to avoid possible DoS attacks)


'''So even if you do not have any changes of routing table, connections may jump to other gateway every 10 minutes'''


[[Category: Manual]]
[[Category: Manual]]

Revision as of 11:19, 27 April 2009

Introduction

Starting from RouterOS version 3.24 there is a new option available in the firewall - PCC (Per Connection Classifier). This option was introduced to address the configuration issues with load balancing over multiple gateways with masquerade

Previous configurations:

PCC takes selected fields from IP header (you can choose from src-address, dst-address, src-port, dst-port) and with a help of hashing algorithm convert selected fields into 32-bit value. This value then is divided by a "Denominator", the remainder then is compared to a specified "Remainder", if equal then packet will be captured. 

per-connection-classifier=
PerConnectionClassifier ::= [!]ValuesToHash:Denominator/Remainder
  Remainder ::= 0..4294967295    (integer number)
  Denominator ::= 1..4294967295    (integer number)
  ValuesToHash ::= src-address|dst-address|src-port|dst-port[,ValuesToHash*]

Example - this configuration will divide all connections into 3 groups based on source address and port 

/ip firewall mangle add chain=prerouting action=mark-connection new-connection-mark=1st_conn per-connection-classifier=src-address,src-port:3/0
/ip firewall mangle add chain=prerouting action=mark-connection new-connection-mark=2nd_conn per-connection-classifier=src-address,src-port:3/1
/ip firewall mangle add chain=prerouting action=mark-connection new-connection-mark=3rd_conn per-connection-classifier=src-address,src-port:3/2

Consider the following network layout:

File:LoadBalancing.jpg

Quick Start for Impatient

Configuration export from the gateway router: 

/ ip address
add address=192.168.0.1/24 network=192.168.0.0 broadcast=192.168.0.255 interface=Local 
add address=10.111.0.2/24 network=10.111.0.0 broadcast=10.111.0.255 interface=wlan2
add address=10.112.0.2/24 network=10.112.0.0 broadcast=10.112.0.255 interface=wlan1

/ ip firewall mangle
add chain=input in-interface=wlan1 action=mark-connection new-connection-mark=wlan1_conn
add chain=input in-interface=wlan2 action=mark-connection new-connection-mark=wlan2_conn
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla1     
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla2     
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/0 \
    action=mark-connection new-connection-mark=wlan1_conn passthrough=yes
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/1 \
    action=mark-connection new-connection-mark=wlan2_conn passthrough=yes
add chain=prerouting connection-mark=wlan1_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan1
add chain=prerouting connection-mark=wlan2_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan2

/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 routing-mark=to_wla1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 routing-mark=to_wla2 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.111.0.1 distance=1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 distance=2 check-gateway=ping

/ ip firewall nat 
add chain=srcnat out-interface=wlan1 action=masquerade
add chain=srcnat out-interface=wlan2 action=masquerade


Explanation

First we give a code snippet and then explain what it actually does.

IP Addresses

/ ip address 
add address=192.168.0.1/24 network=192.168.0.0 broadcast=192.168.0.255 interface=Local
add address=10.111.0.2/24 network=10.111.0.0 broadcast=10.111.0.255 interface=wlan2 
add address=10.112.0.2/24 network=10.112.0.0 broadcast=10.112.0.255 interface=wlan1

The router has two upstream (WAN) interfaces with the addresses of 10.111.0.2/24 and 10.112.0.2/24. The LAN interface has the name "Local" and IP address of 192.168.0.1/24.

Policy routing

First it is necessary to take care of router's traffic - we need to make sure that traffic will leave via same interface it was coming from. We will mark all incoming connections, to remember what was the interface. 

/ ip firewall mangle
add chain=input in-interface=wlan1 action=mark-connection new-connection-mark=wlan1_conn
add chain=input in-interface=wlan2 action=mark-connection new-connection-mark=wlan2_conn

Then we will assign proper routing-mark to the packets leaving the router. 

add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla1     
add chain=output connection-mark=wlan1_conn action=mark-routing new-routing-mark=to_wla2

Action mark-routing can be used only in mangle chain output and prerouting, but mangle chain prerouting is capturing all traffic that is going to the router itself. To avoid this we will use dst-address-type=!local. And with the help of the new PCC we will devide traffic into two groups based on source and destination addressees. 

     
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/0 \
    action=mark-connection new-connection-mark=wlan1_conn passthrough=yes
add chain=prerouting dst-address-type=!local in-interface=Local per-connection-classifier=src-address,dst-address:2/1 \
    action=mark-connection new-connection-mark=wlan2_conn passthrough=yes

Then we need to mark all packets from those connections with a proper mark. As policy routing is required ponly for traffic going to the Internet, do not forget to specify in-interface option. 

add chain=prerouting connection-mark=wlan1_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan1
add chain=prerouting connection-mark=wlan2_conn in-interface=Local action=mark-routing new-routing-mark=to_wlan2

Create a route for each routing-mark 

/ ip route
add dst-address=0.0.0.0/0 gateway=10.111.0.1 routing-mark=to_wla1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 routing-mark=to_wla2 check-gateway=ping

To enable failover, it is necessary to have a routes that will jump in as soon as others will become inactive on gateway failure. (and that will happen only if check-gateway option is active) 

add dst-address=0.0.0.0/0 gateway=10.111.0.1 distance=1 check-gateway=ping
add dst-address=0.0.0.0/0 gateway=10.112.0.1 distance=2 check-gateway=ping

NAT

As routing decision is already made we just need rules that will fix src-addresses for all outgoing packets. if this packet will leave via wlan1 it will be NATed to 10.112.0.2/24, if via wlan2 then NATed to 10.111.0.2/24 

/ ip firewall nat 
add chain=srcnat out-interface=wlan1 action=masquerade
add chain=srcnat out-interface=wlan2 action=masquerade
Retrieved from "https://wiki.mikrotik.com/index.php?title=Manual:PCC&oldid=12182"