<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html><head><title></title>
<META http-equiv=Content-Type content="text/html; charset=iso-8859-1">
<meta http-equiv="Content-Style-Type" content="text/css">
<style type="text/css"><!--
body {
margin: 5px 5px 5px 5px;
background-color: #ffffff;
}
/* ========== Text Styles ========== */
hr { color: #000000}
body, table /* Normal text */
{
font-size: 9pt;
font-family: 'Courier New';
font-style: normal;
font-weight: normal;
color: #000000;
text-decoration: none;
}
span.rvts1 /* Heading */
{
font-size: 10pt;
font-family: 'Arial';
font-weight: bold;
color: #0000ff;
}
span.rvts2 /* Subheading */
{
font-size: 10pt;
font-family: 'Arial';
font-weight: bold;
color: #000080;
}
span.rvts3 /* Keywords */
{
font-size: 10pt;
font-family: 'Arial';
font-style: italic;
color: #800000;
}
a.rvts4, span.rvts4 /* Jump 1 */
{
font-size: 10pt;
font-family: 'Arial';
color: #008000;
text-decoration: underline;
}
a.rvts5, span.rvts5 /* Jump 2 */
{
font-size: 10pt;
font-family: 'Arial';
color: #008000;
text-decoration: underline;
}
span.rvts6
{
font-family: 'tahoma';
font-weight: bold;
color: #ffffff;
background-color: #0000ff;
}
span.rvts7
{
font-family: 'tahoma';
}
a.rvts8, span.rvts8
{
font-family: 'tahoma';
color: #0000ff;
text-decoration: underline;
}
/* ========== Para Styles ========== */
p,ul,ol /* Paragraph Style */
{
text-align: left;
text-indent: 0px;
padding: 0px 0px 0px 0px;
margin: 0px 0px 0px 0px;
}
.rvps1 /* Centered */
{
text-align: center;
}
--></style>
</head>
<body>
<p>Well, I tried it my lab. switchport trunk allowed vlan has no impact on CDP, VTP, LACP, STP etc. They are still sent in vlan 1 even if it is not allowed on trunk.</p>
<p><br></p>
<p><span class=rvts8>http://www.cisco.com/en/US/docs/switches/lan/catalyst2940/software/release/12.1_19_ea1/configuration/guide/swvlan.html#wp1150302</span></p>
<p><br></p>
<p><br></p>
<p> Aivars</p>
<p><br></p>
<div><table border=0 cellpadding=1 cellspacing=2>
<tr valign=top>
<td width=13 style="background-color: #0000ff;">
<p><span class=rvts6>></span></p>
</td>
<td width=1443 style="background-color: #ffffff;">
<p><span class=rvts7>Aivars,</span></p>
<p><br></p>
<p><span class=rvts7>Best practice would be to remove VLAN 1 from the list of trunked VLANs.</span></p>
<p><br></p>
<p><br></p>
<p><br></p>
<p><span class=rvts7>Mike</span></p>
<p><br></p>
<p><br></p>
<p><span class=rvts7>On Mon, Dec 10, 2012 at 10:39 AM, Aivars <</span><a class=rvts8 href="mailto:aivars@ml.lv">aivars@ml.lv</a><span class=rvts7>> wrote:</span></p>
<p><br></p>
<p><span class=rvts7> Hi,</span></p>
<p><br></p>
<p><span class=rvts7> I thought that CDP essence is to help understand what device you</span></p>
<p><span class=rvts7> have at the other end of the wire no matter what. You just plug one</span></p>
<p><span class=rvts7> end of the cable into one box and the other end into another and</span></p>
<p><span class=rvts7> you get your CDP neighbors. Besides other side usage like in IP</span></p>
<p><span class=rvts7> phone communication with switches this is why anybody would use CDP.</span></p>
<p><span class=rvts7> Right?</span></p>
<p><br></p>
<p><span class=rvts7> Up until this morning I also thought that CDP frames are always sent</span></p>
<p><span class=rvts7> untagged. This is the way I would do it. Well, I was wrong. Actually</span></p>
<p><span class=rvts7> on Catalyst switches CDPs are sent in vlan 1. If you make some other</span></p>
<p><span class=rvts7> vlan native on a trunk port, CDPs are sent with dot1q tag "1". vlan</span></p>
<p><span class=rvts7> dot1q tag native will also do the same trick.</span></p>
<p><br></p>
<p><span class=rvts7> Now imagine a brand new shiny IOS-XR box, ASR9k for example. If it</span></p>
<p><span class=rvts7> has no subinterface configuration with encapsulation dot1q 1, CDP</span></p>
<p><span class=rvts7> will be broken. It will send CDPs with no tag and Catalyst will be</span></p>
<p><span class=rvts7> happy about it. It will show ASR as CDP neighbor. ASR instead</span></p>
<p><span class=rvts7> doesn't now what a hell tag "1" means and drop these frames.</span></p>
<p><br></p>
<p><span class=rvts7> Cisco thinks - this is expected behavior.</span></p>
<p><br></p>
<p><span class=rvts7> What do you guys think? Is this a bug or a feature? Should it remain</span></p>
<p><span class=rvts7> as it is?</span></p>
<p><br></p>
<p><span class=rvts7> Aivars</span></p>
<p><br></p>
<p><span class=rvts7>_______________________________________________</span></p>
<p><span class=rvts7>cisco-nsp mailing list </span><a class=rvts8 href="mailto:cisco-nsp@puck.nether.net">cisco-nsp@puck.nether.net</a></p>
<p><a class=rvts8 href="https://puck.nether.net/mailman/listinfo/cisco-nsp">https://puck.nether.net/mailman/listinfo/cisco-nsp</a></p>
<p><span class=rvts7>archive at </span><a class=rvts8 href="http://puck.nether.net/pipermail/cisco-nsp/">http://puck.nether.net/pipermail/cisco-nsp/</a></p>
</td>
</tr>
</table>
</div>
</body></html>