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Manual:OSPF Forwarding Address - Revision history
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Marisb at 12:34, 19 March 2014
2014-03-19T12:34:09Z
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 12:34, 19 March 2014</td>
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Marisb
https://wiki.mikrotik.com/index.php?title=Manual:OSPF_Forwarding_Address&diff=19471&oldid=prev
Marisb at 12:55, 21 October 2010
2010-10-21T12:55:02Z
<p></p>
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<td colspan="2" style="background-color: #fff; color: #202122; text-align: center;">Revision as of 12:55, 21 October 2010</td>
</tr><tr><td colspan="2" class="diff-lineno" id="mw-diff-left-l6">Line 6:</td>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Lets assume that router '''R1''' has static route to external network ''192.168.0.0/24''. OSPF is running between R1,R2 and R3 and static route is distributed across the OSPF network.</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>Lets assume that router '''R1''' has static route to external network ''192.168.0.0/24''. OSPF is running between R1,R2 and R3 and static route is distributed across the OSPF network.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>The problem in such setup is obvious, R2 can not reach external network directly. Traffic from '''R2''' <del style="font-weight: bold; text-decoration: none;">destined to external network </del>will be forwarded to router '''R1'''</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>The problem in such setup is obvious, R2 can not reach external network directly. Traffic from '''R2''' will be forwarded to router '''R1'''</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:ospf-forwarding-traffic.png]]</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>[[File:ospf-forwarding-traffic.png]]</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Fortunately OSPF has mechanism to solve such situations. OSPF router can set '''forwarding address''' to something other than itself which indicates that alternate nexthop is possible. Mostly forwarding address is set to 0.0.0.0 suggesting that the route is reachable only via the advertising router.</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Fortunately OSPF has mechanism to solve such situations. OSPF router can set '''forwarding<ins style="font-weight: bold; text-decoration: none;">-</ins>address''' to something other than itself which indicates that alternate nexthop is possible. Mostly forwarding address is set to <ins style="font-weight: bold; text-decoration: none;"> '''</ins>0.0.0.0<ins style="font-weight: bold; text-decoration: none;">''' </ins>suggesting that the route is reachable only via the advertising router.</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>Forwarding address is set in LSA <del style="font-weight: bold; text-decoration: none;">only </del>if following conditions are met:</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>Forwarding address is set in LSA<ins style="font-weight: bold; text-decoration: none;">, </ins>if following conditions are met:</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><ul class="bullets"></div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><ul class="bullets"></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><li>OSPF must be enabled on next-hop interface</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><li>OSPF must be enabled on next-hop interface</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>So knowing conditions <del style="font-weight: bold; text-decoration: none;">in our example setup </del>we can make router '''R1''' to set forwarding address. We simply need to add 10.1.101.0/24 network to OSPF networks <del style="font-weight: bold; text-decoration: none;">on </del>R1:</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>So knowing conditions<ins style="font-weight: bold; text-decoration: none;">, </ins>we can make router '''R1''' to set forwarding address. We simply need to add 10.1.101.0/24 network to OSPF networks <ins style="font-weight: bold; text-decoration: none;">in router's '''</ins>R1<ins style="font-weight: bold; text-decoration: none;">''' configuration</ins>:</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><pre></div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div><pre></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>/routing ospf network add network=10.1.101.0/24 area=backbone</div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div>/routing ospf network add network=10.1.101.0/24 area=backbone</div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div></pre></div></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><div></pre></div></td></tr>
<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
<tr><td class="diff-marker" data-marker="−"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #ffe49c; vertical-align: top; white-space: pre-wrap;"><div>{{Note | OSPF adjacency between <del style="font-weight: bold; text-decoration: none;">router </del>in 10.1.101.0/24 network is not required}}</div></td><td class="diff-marker" data-marker="+"></td><td style="color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #a3d3ff; vertical-align: top; white-space: pre-wrap;"><div>{{Note | OSPF adjacency between <ins style="font-weight: bold; text-decoration: none;">routers </ins>in 10.1.101.0/24 network is not required}}</div></td></tr>
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<tr><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td><td class="diff-marker"></td><td style="background-color: #f8f9fa; color: #202122; font-size: 88%; border-style: solid; border-width: 1px 1px 1px 4px; border-radius: 0.33em; border-color: #eaecf0; vertical-align: top; white-space: pre-wrap;"><br/></td></tr>
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Marisb
https://wiki.mikrotik.com/index.php?title=Manual:OSPF_Forwarding_Address&diff=19468&oldid=prev
Marisb: Created page with '{{Versions|v3, v4, v5 +}} File:ospf-forwarding.png Lets assume that router '''R1''' has static route to external network ''192.168.0.0/24''. OSPF is running between R1,R2 …'
2010-10-21T12:33:51Z
<p>Created page with '{{Versions|v3, v4, v5 +}} <a href="/wiki/File:Ospf-forwarding.png" title="File:Ospf-forwarding.png">File:ospf-forwarding.png</a> Lets assume that router '''R1''' has static route to external network ''192.168.0.0/24''. OSPF is running between R1,R2 …'</p>
<p><b>New page</b></p><div>{{Versions|v3, v4, v5 +}}<br />
<br />
<br />
[[File:ospf-forwarding.png]]<br />
<br />
Lets assume that router '''R1''' has static route to external network ''192.168.0.0/24''. OSPF is running between R1,R2 and R3 and static route is distributed across the OSPF network.<br />
<br />
The problem in such setup is obvious, R2 can not reach external network directly. Traffic from '''R2''' destined to external network will be forwarded to router '''R1'''<br />
<br />
[[File:ospf-forwarding-traffic.png]]<br />
<br />
<br />
<pre><br />
[admin@R2] /ip route> print <br />
Flags: X - disabled, A - active, D - dynamic, <br />
C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, <br />
B - blackhole, U - unreachable, P - prohibit <br />
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE<br />
... <br />
8 ADo 192.168.0.0/24 10.1.101.10 110<br />
</pre><br />
<br />
<br />
Fortunately OSPF has mechanism to solve such situations. OSPF router can set '''forwarding address''' to something other than itself which indicates that alternate nexthop is possible. Mostly forwarding address is set to 0.0.0.0 suggesting that the route is reachable only via the advertising router.<br />
<br />
Forwarding address is set in LSA only if following conditions are met:<br />
<ul class="bullets"><br />
<li>OSPF must be enabled on next-hop interface<br />
<li>Interface is not passive<br />
<li>Interface is not p2p or p2mp<br />
<li>Next-hop address falls into network provided in ospf networks<br />
</ul><br />
<br />
So knowing conditions in our example setup we can make router '''R1''' to set forwarding address. We simply need to add 10.1.101.0/24 network to OSPF networks on R1:<br />
<pre><br />
/routing ospf network add network=10.1.101.0/24 area=backbone<br />
</pre><br />
<br />
{{Note | OSPF adjacency between router in 10.1.101.0/24 network is not required}}<br />
<br />
<br />
Now lets verify that forwarding address is actually working:<br />
<pre><br />
[admin@R2] /ip route> print <br />
Flags: X - disabled, A - active, D - dynamic, <br />
C - connect, S - static, r - rip, b - bgp, o - ospf, m - mme, <br />
B - blackhole, U - unreachable, P - prohibit <br />
# DST-ADDRESS PREF-SRC GATEWAY DISTANCE<br />
... <br />
8 ADo 192.168.0.0/24 10.1.101.1 110<br />
</pre><br />
<br />
On all OSPF routers you will see LSA set with forwarding address other than 0.0.0.0<br />
<pre><br />
[admin@R2] /routing ospf lsa>print detail<br />
instance=default area=external type=as-external id=192.168.0.0 <br />
originator=10.1.101.1 sequence-number=0x80000073 age=16 checksum=0x8510 <br />
options="E" body=<br />
netmask=255.255.255.0<br />
forwarding-address=10.1.101.1<br />
metric=30<br />
route-tag=0x0<br />
type1<br />
</pre><br />
<br />
<br />
{{cont}}<br />
<br />
[[Category:Manual|O]]<br />
[[Category:Routing|O]]<br />
[[Category:Case Studies|O]]</div>
Marisb