The Unicast Reverse Path Forwarding (Unicast RPF) in Strict Mode feature is a .. Figure 2 Unicast RPF Dropping Packets That Fail Verification .. not imply a partnership relationship between Cisco and any other company. Internet-Draft Unicast RPF Experiences January Table of Contents 1. The same considerations also apply for other business relationships (e.g., "internal . These packets fail uRPF check at R2 (and vice versa at R1). Assuming a strictly symmetric routing, is there any difference between using antispoof rules and blocking incoming packets that fail the unicast.
The list of Internet-Draft Shadow Directories can be accessed at http: This Internet-Draft will expire on July 26, This memo tries to document operational experiences learned practising ingress filtering techniques, in particular ingress filtering for multihomed networks.
Unused Address Space Ping-Pong. Incorrect Source Address Selection. Specifically, this version describes the lessons learned in author's network where strict unicast RPF uRPF ingress filtering, using "feasible paths" variant [ RFC ] has been used for all the customer interfaces whether single- or multihomed since In feasible paths strict uRPF, only an accepted equal length prefix even if not preferred is considered feasible.
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Although in some cases a more specific or even a less specific might be acceptable, such condition would not necessarily be correct in general. We use the typical "customer" and "ISP" terms to refer to the subject of strict uRPF filtering and the party doing filtering. The same considerations also apply for other business relationships e.
We note explicitly that Loose mode RPF is NOT a sufficient solution in any way to ingress filtering as it creates a false sense of protection.
Even its use as a "contract validation" [ RFC ] is tenuous at best. However, it is not clear what should be the next steps wrt. Update to the ingress filtering RFCs? Keep as a standing document for now?
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In any case, feedback on other experiences is encouraged. In the second section, we'll first look at the most common types of uRPF drops and their causes. In the third section, we'll look at a few special cases observed on multihoming or multi-connecting scenarios.
More special filtering failures are discussed in the fourth section. In this section, we'll describe the most common causes for uRPF drops which apply to both single- and multi-homed networks, and respective ways to eliminate or mitigate dropping. In this case, typically packets destined to the unused part of "P" lack a more specific route, and are forwarded back to the ISP through a default route.
This fails uRPF check and is dropped. This has been briefly described in [ I-D.Why Modern Relationships Fail - The View
Hence employing uRPF significantly mitigates the impact of this kind of packet looping. The ping-pong effect has also been used in Internet Exchanges to game peer selection or traffic balance data. Therefore, the customer should install static discard aggregate routes or equivalent for all of its address space upon assignment, so that if no better route exists, such probe packets are discarded. An alternative is applying a similar filtering in egress interface towards the ISP.
Understanding How Unicast Reverse Path Forwarding Prevents Spoofed IP Packet Forwarding
This is probably a result of misconfigured NATs or inadequate firewall rules. Even constant rates of hundreds of packets per second have been observed, which makes one wonder which kinds of users' communications must be failing or otherwise working in a non-optimal fashion due to this kind of misconfiguration This is actually one of the most convincing reasons from the users' perspective why they or the ISP using uRPF could give benefits: The obvious fix is to ensure that the customer is filtering out and logging these packets, and uses that to figure out what is causing such address leaks and fixes the misconfiguration or other problem s.
Wrong IP Address It's also not atypical to see other kinds of wrong source addresses. These can be classified in three main categories: It should be noted that Loose uRPF would only spot the last category.
Many spoofed attacks are usually a result of a worm or a botnet DoS attack. The same considerations as for leaking private addresses apply here, except that these wouldn't typically get this far if the customer had been using unicast RPF at its LAN interfaces -- uRPF can and should be applied recursively [ RFC ]. Bearing these in mind, uRPF can be employed with multihomed networks as well. We note that a customer can multihome and even perform traffic engineering with feasible paths uRPF provided that the consistency requirement is fulfilled.
In other words, AS-path prepending, setting communities to lower local-preference, etc. The same applies to networks with multiple prefixes as explored in [ I-D. When a host in P1 sends a packet to A2, the response may go out through interface 1; similarly, when a host in P2 sends a packet to A1, the response may go out through interface 2. But if things seem to be more down than up when you look at an important relationship in your life--whether it's a colleague or a friend, a key employee or a business partner--you may start to wonder if something more serious is going on.
Here are some symptoms that should cause you concern, together with the preventive measures that can help you keep your relationships healthy: Resentment grows when someone feels unheard or dismissed.
Left unchecked, it leads to bitterness and a smoldering anger that scorches everything around it. Communication goes from difficult to impossible and negativity is overwhelming. The best prevention is a combination of equity and communication.
Make sure everything, from cash to household or office responsibilities, is handled fairly, and if there's something on your mind or you're feeling frustrated by a situation, talk about it. Mutual respect is a cornerstone of all successful relationships. If you're sensing disrespect, whether you're giving it or receiving, you have a fundamental problem.
It's sometimes a case of never having learned how to disagree respectfully, and at other times a more serious or personal issue. An occasional lie is forgivable--and, depending on your moral outlook and the situation, sometimes even appropriate--but lies about serious matters, or a daily barrage of deception, are seriously harmful.
Often a key to the source lies in asking yourselves what function the lies are playing. Is it to give an illusion of competence in some area, or to prop up a failing sense of self-respect?
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Once you understand why, you can find more positive ways to achieve the same end. A single betrayal--or an act perceived as a betrayal--can wipe out a lifetime of trust. If trust is absent, again, ask why? Is it warranted, or is it coming from something unresolved in in a past relationship? If there has been a breach, is it too serious to be mended? If one or both partners is consistently tuning out, seeking distractions, and making a conscious effort to avoid making a connection, it may be that the bond between you has already been severed.