Priscilla Oppenheimer <[EMAIL PROTECTED]> wrote: > At 06:07 PM 3/6/01, NetEng wrote: > >Does HSRP work at the interface level or is the entire router on > >acvtive/stand-by? In other words, if I have two routers working in HSRP and > >a link goes down somewhere down the line, will the first router know to > >fail-over to the second router (with a good link)? HSRP works at the interface level by definition. It is configured at the interface level, too. If a link goes down "somewhere down the line", that is NOT a function of HSRP failover. However, if a directly connected link fails, it CAN switch itself to another standby router. Here are your HSRP failover parameters: 1. Loss of direct interface - all traffic is shifted to another standby interface. 2. Loss of interface(s) directly attached in that router (by use of the "standby track <interface>" command - HSRP can track multiple interfaces simultaneously 3. HSRP does NOT disable the primary IP address on a standby interface, nor does it squelch routing updates from those interfaces. All HSRP interfaces are ALWAYS live on their primary IP address. Therefore, it's conceivable that rerouting could occur if a downstream path were broken and you had multiple default gateway addresses programmed on your hosts. However, enabling HSRP also DISABLES ICMP redirects (to prevent routing loops... ha-ha-ha-ha) and you can't run it with Proxy ARP, so you end up having to make a decision about how best to enable redundancy/failover on your network. > > Interesting question. The first router would have to lose its connectivity > to the second router. Routers that are running HSRP send and receive > multicast UDP-based hello packets to detect router failure and to designate > active and standby routers. HSRP detects when the designated active router > fails because of the lack of hello packets, at which point a selected > standby router assumes control of the Hot Standby group's MAC and IP > addresses. A new standby router is also selected at that time. > > Remember HSRP stands for Hot Standby Router Protocol, not Hot Standby > Routing protocol. It's the default router for LAN devices that's on > standby. If you think of HSRP as a routing protocol, then you will tend to > think it does more than it does. I think to solve your problem you need a > "real" routing protocol, although without more info, it's hard to say for > sure. BTW, nothing throws off HSRP worst than losing connectivity between the standby interfaces when they're still all active. Dynamic routing tables go berserk, because they receive the same routing update from two different sources and that sometimes starts the asymmetric routing dance. > > Priscilla > > > I have one router > >connected to one ISP and a second router connected to a second ISP. Can > >these routers be run in HSRP or must they be running in parallel and let a > >dynamic routing protocol (BGP on the outside and let's say EIGRP on the > >inside) decide? TIA. > > > > > >_________________________________ > >FAQ, list archives, and subscription info: > >http://www.groupstudy.com/list/cisco.html > >Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] > > > ________________________ > > Priscilla Oppenheimer > http://www.priscilla.com > > _________________________________ > FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html > Report misconduct and Nondisclosure violations to [EMAIL PROTECTED] ____________________________________________________________________ Get free email and a permanent address at http://www.netaddress.com/?N=1 _________________________________ FAQ, list archives, and subscription info: http://www.groupstudy.com/list/cisco.html Report misconduct and Nondisclosure violations to [EMAIL PROTECTED]
