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<span style="font-family: Calibri, sans-serif; font-size: 14.6667px; display: inline !important; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);">Hi birds,</span><br>
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<div style="" class="elementToProof"><font face="Calibri, sans-serif" style="color: rgb(36, 36, 36);"><span style="font-size: 14.6667px;">This is the detailed explanation of the previously raised issue. <br>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0">We are using BIRD<span class="ContentPasted0"> </span><a href="https://gitlab.nic.cz/labs/bird/-/tags/v2.0.11" target="_blank" rel="noopener noreferrer" data-auth="NotApplicable" data-linkindex="0" style="margin: 0px; text-decoration: underline; color: rgb(5, 99, 193);" class="ContentPasted0">https://gitlab.nic.cz/labs/bird/-/tags/v2.0.11</a>.
And there is an issue with respect to BFD + BGP as described below.</span></p>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0"> </span></p>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0">When Peer device ( Cisco ASR router) sends an BFD admin down, Bird is bringing down the BGP connection which is using BFD mode ON, which is not correct. The expected behavior is upon receiving BFD
admin down from peer device, Bird should fall back to the Normal BGP mode of working.</span></p>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0"> </span></p>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0"> </span></p>
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<span lang="EN-US" style="margin:0px" class="ContentPasted0">As per the comment mentioned on Bird forum, We could see the same (expected behavior) is to be claimed as ways of working for Bird:</span></p>
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That is expected.<span class="ContentPasted0"> </span><b class="ContentPasted0">Only a BFD transition from Up to Down is supposed to<br class="ContentPasted0">
shutdown the BGP or OSPF session, while general unavailability of BFD<br class="ContentPasted0">
(or permanent AdminDown state) on the neighbor is not an obstacle for<br class="ContentPasted0">
BGP or OSPF</b>. See<span class="ContentPasted0"> </span><b><span style="margin: 0px; color: rgb(68, 114, 196);" class="ContentPasted0">RFC 5882</span></b><span style="margin: 0px; color: rgb(68, 114, 196);"><span class="ContentPasted0"> </span></span>for details. </p>
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<a href="https://bird-users.network.narkive.com/3REbA0Wz/bfd-implementation-in-1-4-0#post5" target="_blank" rel="noopener noreferrer" data-auth="NotApplicable" title="https://bird-users.network.narkive.com/3reba0wz/bfd-implementation-in-1-4-0#post5" data-linkindex="1" style="margin: 0px; text-decoration: underline; color: rgb(5, 99, 193);" class="ContentPasted0" data-loopstyle="linkonly">BFD
implementation in 1.4.0 (narkive.com)</a></p>
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</p>
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Steps:</p>
<ol type="1" style="margin-bottom: 0cm; font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);" data-listchain="__List_Chain_29">
<li style="margin-left:54pt" class="ContentPasted0">Setup Bird config as (single hop / directly connected to router):</li></ol>
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<img width="367" height="614" alt="protocol device {
}
protocol bgp {
local 10.0.10.22 as 64512;
neighbor 10.0.10.6 as 65001;
hold time 3;
graceful restart off;
setkey off;
ipv4 {
import all;
export filter {
if proto = "static1" then reject;
accept;
};
};
bfd on;
}
protocol bfd {
interface "eth0" {
min rx interval 100 ms;
min tx interval 100 ms;
idle tx interval 300 ms;
multiplier 3;
};
neighbor 10.0.10.6;
neighbor 10.0.10.8;
neighbor 10.0.10.10;
}
" class="Do8Zj ContentPasted0 w-550 h-921" style="margin:0px;animation:0.1s ease-out 0s 1 normal none running Do8Zj;width:3.8194in;height:6.3958in;min-height:auto;min-width:auto;cursor:pointer" size="51860" contenttype="image/png" data-outlook-trace="F:1|T:1" src="cid:2c6f7097-3741-438e-880b-5e1376328ff2"></p>
<ol start="2" type="1" style="margin-bottom: 0cm; font-family: "Segoe UI", "Segoe UI Web (West European)", "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, "Helvetica Neue", sans-serif; font-size: 15px; color: rgb(36, 36, 36); background-color: rgb(255, 255, 255);" data-listchain="__List_Chain_29">
<li style="margin-left:54pt" class="ContentPasted0">Make sure BGP and BFD session are up between bird and DCGW/router.</li><li style="margin-left:54pt" class="ContentPasted0">From router bring down the BFD session alone.</li><li style="margin-left:54pt" class="ContentPasted0">On Bird end we observe BGP session was brought down upon receiving BFD admin down. Which is not expected behaviour as per RFC.</li></ol>
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<br>
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As per<span class="ContentPasted0"> </span><a href="https://datatracker.ietf.org/doc/html/rfc5882#section-3.2" target="_blank" rel="noopener noreferrer" data-auth="NotApplicable" data-linkindex="2" style="margin: 0px; text-decoration: underline; color: rgb(5, 99, 193);" class="ContentPasted0" data-loopstyle="linkonly">rfc5882#section-3.2</a></p>
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<br>
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<i><span style="margin: 0px; color: black;" class="ContentPasted0">Therefore, a system<span class="ContentPasted0"> </span><b class="ContentPasted0">SHOULD NOT</b><span class="ContentPasted0"> </span>indicate a connectivity failure to a</span></i><i><span style="margin:0px"></span></i></p>
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<i><span style="margin: 0px; color: black;" class="ContentPasted0"> client if either the local session state or the remote session state</span></i><i><span style="margin:0px"></span></i></p>
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<i><span style="margin: 0px; color: black;" class="ContentPasted0"> (if known) transitions to AdminDown, so long as that client has</span></i><i><span style="margin:0px"></span></i></p>
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<i><span style="margin: 0px; color: black;" class="ContentPasted0"> independent means of liveness detection (typically, control</span></i><i><span style="margin:0px"></span></i></p>
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<i><span style="margin: 0px; color: black;" class="ContentPasted0"> protocols).</span></i><i><span style="margin:0px"></span></i></p>
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</p>
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Attached PCAP : 128.0.0.3 is the router IP address and 128.0.0.53 is the Bird IP.</p>
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<br>
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Br,<br>
Sunnat Samadov</p>
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