Hi,
TOS refers to Type of Service, which used to be a field in the IP header. That field has now been superceded by the DSCP field.
Older versions of OSPF used to support routing based on different values of the TOS bits. The current version of OSPF does not support that and uses zero in the fields which required a TOS value. That is why you see the TOS0 in the output of sh ip ospf.
Pls do remember to rate posts.
Paresh
