On r2851 - 12.4.17 AdvSec there is a Serial link with Multilink (due fragmentation for VoIP) and backup ISDN-BRI line. When we shutdown the Serial IF, backup ISDN comes up. When we bring Serial IF back to up with no shut, IF comes up but protocol is still down as well Multilink is down/down. ISDN BRI remain up till we bring it down manually. Is there any limitation with using Multilink in backup scenario?
Thanks for advise