How to show the parent site in the breadcrumb of your custom masterpage?
By default there is a masterpage that has this configuration. You can find this in the default nightandday.master.
What needs to be done to have this in your custom masterpage?
Add following code to in the <div class="s4-ca"> tag:
<!-- Breadcrumb with parent site -->
<div class="breadcrumb">
<asp:SiteMapPath
runat="server"
SiteMapProviders="SPSiteMapProvider,SPXmlContentMapProvider"
RenderCurrentNodeAsLink="false"
NodeStyle-CssClass="breadcrumbNode"
CurrentNodeStyle-CssClass="breadcrumbCurrentNode"
RootNodeStyle-CssClass="breadcrumbRootNode"
HideInteriorRootNodes="true"
SkipLinkText="" />
</div>
The css here defined contains the default style of the v4.master headbreadcrumb.